WARNING: bad usercopy in fanotify_read

WARNING: bad usercopy in fanotify_read

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    12ad143e Merge branch 'perf-urgent-for-linus' of git://git..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12776f57200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e9d91b7192a5e96e
dashboard link: https://syzkaller.appspot.com/bug?extid=2c49971e251e36216d1f
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: amd64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1287516f200000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com

------------[ cut here ]------------
Bad or missing usercopy whitelist? Kernel memory exposure attempt detected  
from SLAB object 'fanotify_event' (offset 40, size 8)!
WARNING: CPU: 1 PID: 7649 at mm/usercopy.c:78 usercopy_warn+0xeb/0x110  
mm/usercopy.c:78
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 7649 Comm: syz-executor381 Not tainted 5.0.0+ #17
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x172/0x1f0 lib/dump_stack.c:113
  panic+0x2cb/0x65c kernel/panic.c:214
  __warn.cold+0x20/0x45 kernel/panic.c:571
  report_bug+0x263/0x2b0 lib/bug.c:186
  fixup_bug arch/x86/kernel/traps.c:179 [inline]
  fixup_bug arch/x86/kernel/traps.c:174 [inline]
  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:272
  do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:291
  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
RIP: 0010:usercopy_warn+0xeb/0x110 mm/usercopy.c:78
Code: c8 e8 d9 88 c0 ff 4c 8b 45 c0 4d 89 e9 4c 89 e1 48 8b 55 c8 41 57 48  
89 de 48 c7 c7 e0 dc 74 87 ff 75 d0 41 56 e8 03 4b 93 ff <0f> 0b 48 83 c4  
18 e9 46 ff ff ff 49 c7 c5 e0 da 74 87 4d 89 ee 4d
RSP: 0018:ffff8880a417fb18 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffffffff8774dca0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff815ad7b6 RDI: ffffed101482ff55
RBP: ffff8880a417fb70 R08: ffff888088d78580 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff8859408d
R13: ffffffff8775d500 R14: ffffffff8774db20 R15: 0000000000000008
  __check_heap_object+0x88/0xb3 mm/slab.c:4453
  check_heap_object mm/usercopy.c:238 [inline]
  __check_object_size mm/usercopy.c:284 [inline]
  __check_object_size+0x342/0x42f mm/usercopy.c:254
  check_object_size include/linux/thread_info.h:119 [inline]
  check_copy_size include/linux/thread_info.h:150 [inline]
  copy_to_user include/linux/uaccess.h:151 [inline]
  copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
  copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]
  fanotify_read+0xde0/0x1430 fs/notify/fanotify/fanotify_user.c:362
  __vfs_read+0x8d/0x110 fs/read_write.c:416
  vfs_read+0x194/0x3e0 fs/read_write.c:452
  ksys_read+0xea/0x1f0 fs/read_write.c:578
  __do_sys_read fs/read_write.c:588 [inline]
  __se_sys_read fs/read_write.c:586 [inline]
  __x64_sys_read+0x73/0xb0 fs/read_write.c:586
  do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4456b9
Code: e8 6c b6 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 2b 12 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fb296f31db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00000000006dac28 RCX: 00000000004456b9
RDX: 000000000000006b RSI: 0000000020000000 RDI: 0000000000000004
RBP: 00000000006dac20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dac2c
R13: 00007ffd8eb3d16f R14: 00007fb296f329c0 R15: 20c49ba5e353f7cf
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with  
syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

WARNING: bad usercopy in fanotify_read

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    12ad143e Merge branch 'perf-urgent-for-linus' of git://git..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12776f57200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e9d91b7192a5e96e
dashboard link: https://syzkaller.appspot.com/bug?extid=2c49971e251e36216d1f
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: amd64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1287516f200000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com

------------[ cut here ]------------
Bad or missing usercopy whitelist? Kernel memory exposure attempt detected  
from SLAB object 'fanotify_event' (offset 40, size 8)!
WARNING: CPU: 1 PID: 7649 at mm/usercopy.c:78 usercopy_warn+0xeb/0x110  
mm/usercopy.c:78
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 7649 Comm: syz-executor381 Not tainted 5.0.0+ #17
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x172/0x1f0 lib/dump_stack.c:113
  panic+0x2cb/0x65c kernel/panic.c:214
  __warn.cold+0x20/0x45 kernel/panic.c:571
  report_bug+0x263/0x2b0 lib/bug.c:186
  fixup_bug arch/x86/kernel/traps.c:179 [inline]
  fixup_bug arch/x86/kernel/traps.c:174 [inline]
  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:272
  do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:291
  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
RIP: 0010:usercopy_warn+0xeb/0x110 mm/usercopy.c:78
Code: c8 e8 d9 88 c0 ff 4c 8b 45 c0 4d 89 e9 4c 89 e1 48 8b 55 c8 41 57 48  
89 de 48 c7 c7 e0 dc 74 87 ff 75 d0 41 56 e8 03 4b 93 ff <0f> 0b 48 83 c4  
18 e9 46 ff ff ff 49 c7 c5 e0 da 74 87 4d 89 ee 4d
RSP: 0018:ffff8880a417fb18 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffffffff8774dca0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff815ad7b6 RDI: ffffed101482ff55
RBP: ffff8880a417fb70 R08: ffff888088d78580 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff8859408d
R13: ffffffff8775d500 R14: ffffffff8774db20 R15: 0000000000000008
  __check_heap_object+0x88/0xb3 mm/slab.c:4453
  check_heap_object mm/usercopy.c:238 [inline]
  __check_object_size mm/usercopy.c:284 [inline]
  __check_object_size+0x342/0x42f mm/usercopy.c:254
  check_object_size include/linux/thread_info.h:119 [inline]
  check_copy_size include/linux/thread_info.h:150 [inline]
  copy_to_user include/linux/uaccess.h:151 [inline]
  copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
  copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]
  fanotify_read+0xde0/0x1430 fs/notify/fanotify/fanotify_user.c:362
  __vfs_read+0x8d/0x110 fs/read_write.c:416
  vfs_read+0x194/0x3e0 fs/read_write.c:452
  ksys_read+0xea/0x1f0 fs/read_write.c:578
  __do_sys_read fs/read_write.c:588 [inline]
  __se_sys_read fs/read_write.c:586 [inline]
  __x64_sys_read+0x73/0xb0 fs/read_write.c:586
  do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4456b9
Code: e8 6c b6 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 2b 12 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fb296f31db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00000000006dac28 RCX: 00000000004456b9
RDX: 000000000000006b RSI: 0000000020000000 RDI: 0000000000000004
RBP: 00000000006dac20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dac2c
R13: 00007ffd8eb3d16f R14: 00007fb296f329c0 R15: 20c49ba5e353f7cf
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with  
syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

Re: WARNING: bad usercopy in fanotify_read

[Kees Cook]

On Mon, Mar 11, 2019 at 1:42 PM syzbot
<syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com> wrote:
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000
> [...]
> ------------[ cut here ]------------
> Bad or missing usercopy whitelist? Kernel memory exposure attempt detected
> from SLAB object 'fanotify_event' (offset 40, size 8)!
> [...]
>   copy_to_user include/linux/uaccess.h:151 [inline]
>   copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
>   copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]

Looks like this is the fh/ext_fh union in struct fanotify_fid, field
"fid" in struct fanotify_event. Given that "fid" is itself in a union
against a struct path, I think instead of a whitelist using
KMEM_CACHE_USERCOPY(), this should just use a bounce buffer to avoid
leaving a whitelist open for path or ext_fh exposure.

Maybe something like this (untested):

diff --git a/fs/notify/fanotify/fanotify_user.c
b/fs/notify/fanotify/fanotify_user.c
index 56992b32c6bb..b87da9580b3c 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -207,6 +207,7 @@ static int process_access_response(struct
fsnotify_group *group,
 static int copy_fid_to_user(struct fanotify_event *event, char __user *buf)
 {
        struct fanotify_event_info_fid info = { };
+       unsigned char bounce[FANOTIFY_INLINE_FH_LEN], *fh;
        struct file_handle handle = { };
        size_t fh_len = event->fh_len;
        size_t len = fanotify_event_info_len(event);
@@ -233,7 +234,18 @@ static int copy_fid_to_user(struct fanotify_event
*event, char __user *buf)

        buf += sizeof(handle);
        len -= sizeof(handle);
-       if (copy_to_user(buf, fanotify_event_fh(event), fh_len))
+
+       /*
+        * For an inline fh, copy through stack to exclude the copy from
+        * usercopy hardening protections.
+        */
+       fh = fanotify_event_fh(event);
+       if (fh_len <= sizeof(bounce)) {
+               memcpy(bounce, fh, fh_len);
+               fh = bounce;
+       }
+
+       if (copy_to_user(buf, fh, fh_len))
                return -EFAULT;

        /* Pad with 0's */


-- 
Kees Cook

Re: WARNING: bad usercopy in fanotify_read

[Kees Cook]

On Mon, Mar 11, 2019 at 1:42 PM syzbot
<syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com> wrote:
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000
> [...]
> ------------[ cut here ]------------
> Bad or missing usercopy whitelist? Kernel memory exposure attempt detected
> from SLAB object 'fanotify_event' (offset 40, size 8)!
> [...]
>   copy_to_user include/linux/uaccess.h:151 [inline]
>   copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
>   copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]

Looks like this is the fh/ext_fh union in struct fanotify_fid, field
"fid" in struct fanotify_event. Given that "fid" is itself in a union
against a struct path, I think instead of a whitelist using
KMEM_CACHE_USERCOPY(), this should just use a bounce buffer to avoid
leaving a whitelist open for path or ext_fh exposure.

Maybe something like this (untested):

diff --git a/fs/notify/fanotify/fanotify_user.c
b/fs/notify/fanotify/fanotify_user.c
index 56992b32c6bb..b87da9580b3c 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -207,6 +207,7 @@ static int process_access_response(struct
fsnotify_group *group,
 static int copy_fid_to_user(struct fanotify_event *event, char __user *buf)
 {
        struct fanotify_event_info_fid info = { };
+       unsigned char bounce[FANOTIFY_INLINE_FH_LEN], *fh;
        struct file_handle handle = { };
        size_t fh_len = event->fh_len;
        size_t len = fanotify_event_info_len(event);
@@ -233,7 +234,18 @@ static int copy_fid_to_user(struct fanotify_event
*event, char __user *buf)

        buf += sizeof(handle);
        len -= sizeof(handle);
-       if (copy_to_user(buf, fanotify_event_fh(event), fh_len))
+
+       /*
+        * For an inline fh, copy through stack to exclude the copy from
+        * usercopy hardening protections.
+        */
+       fh = fanotify_event_fh(event);
+       if (fh_len <= sizeof(bounce)) {
+               memcpy(bounce, fh, fh_len);
+               fh = bounce;
+       }
+
+       if (copy_to_user(buf, fh, fh_len))
                return -EFAULT;

        /* Pad with 0's */


-- 
Kees Cook

Re: WARNING: bad usercopy in fanotify_read

[Amir Goldstein]

On Wed, Mar 13, 2019 at 8:26 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Mon, Mar 11, 2019 at 1:42 PM syzbot
> <syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com> wrote:
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000
> > [...]
> > ------------[ cut here ]------------
> > Bad or missing usercopy whitelist? Kernel memory exposure attempt detected
> > from SLAB object 'fanotify_event' (offset 40, size 8)!
> > [...]
> >   copy_to_user include/linux/uaccess.h:151 [inline]
> >   copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
> >   copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]
>
> Looks like this is the fh/ext_fh union in struct fanotify_fid, field
> "fid" in struct fanotify_event. Given that "fid" is itself in a union
> against a struct path, I think instead of a whitelist using
> KMEM_CACHE_USERCOPY(), this should just use a bounce buffer to avoid
> leaving a whitelist open for path or ext_fh exposure.
>
> Maybe something like this (untested):

I tested. Patch is fine by me with minor nit.
You may add:
Reviewed-by: Amir Goldstein <amir73il@gmail.com>


>
> diff --git a/fs/notify/fanotify/fanotify_user.c
> b/fs/notify/fanotify/fanotify_user.c
> index 56992b32c6bb..b87da9580b3c 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -207,6 +207,7 @@ static int process_access_response(struct
> fsnotify_group *group,
>  static int copy_fid_to_user(struct fanotify_event *event, char __user *buf)
>  {
>         struct fanotify_event_info_fid info = { };
> +       unsigned char bounce[FANOTIFY_INLINE_FH_LEN], *fh;
>         struct file_handle handle = { };
>         size_t fh_len = event->fh_len;
>         size_t len = fanotify_event_info_len(event);
> @@ -233,7 +234,18 @@ static int copy_fid_to_user(struct fanotify_event
> *event, char __user *buf)
>
>         buf += sizeof(handle);
>         len -= sizeof(handle);
> -       if (copy_to_user(buf, fanotify_event_fh(event), fh_len))
> +
> +       /*
> +        * For an inline fh, copy through stack to exclude the copy from
> +        * usercopy hardening protections.
> +        */
> +       fh = fanotify_event_fh(event);
> +       if (fh_len <= sizeof(bounce)) {

Prefer <= FANOTIFY_INLINE_FH_LEN

> +               memcpy(bounce, fh, fh_len);
> +               fh = bounce;
> +       }
> +
> +       if (copy_to_user(buf, fh, fh_len))
>                 return -EFAULT;
>
>         /* Pad with 0's */
>
>
> --
> Kees Cook

Re: WARNING: bad usercopy in fanotify_read

[Amir Goldstein]

On Wed, Mar 13, 2019 at 8:26 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Mon, Mar 11, 2019 at 1:42 PM syzbot
> <syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com> wrote:
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000
> > [...]
> > ------------[ cut here ]------------
> > Bad or missing usercopy whitelist? Kernel memory exposure attempt detected
> > from SLAB object 'fanotify_event' (offset 40, size 8)!
> > [...]
> >   copy_to_user include/linux/uaccess.h:151 [inline]
> >   copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
> >   copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]
>
> Looks like this is the fh/ext_fh union in struct fanotify_fid, field
> "fid" in struct fanotify_event. Given that "fid" is itself in a union
> against a struct path, I think instead of a whitelist using
> KMEM_CACHE_USERCOPY(), this should just use a bounce buffer to avoid
> leaving a whitelist open for path or ext_fh exposure.
>
> Maybe something like this (untested):

I tested. Patch is fine by me with minor nit.
You may add:
Reviewed-by: Amir Goldstein <amir73il@gmail.com>


>
> diff --git a/fs/notify/fanotify/fanotify_user.c
> b/fs/notify/fanotify/fanotify_user.c
> index 56992b32c6bb..b87da9580b3c 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -207,6 +207,7 @@ static int process_access_response(struct
> fsnotify_group *group,
>  static int copy_fid_to_user(struct fanotify_event *event, char __user *buf)
>  {
>         struct fanotify_event_info_fid info = { };
> +       unsigned char bounce[FANOTIFY_INLINE_FH_LEN], *fh;
>         struct file_handle handle = { };
>         size_t fh_len = event->fh_len;
>         size_t len = fanotify_event_info_len(event);
> @@ -233,7 +234,18 @@ static int copy_fid_to_user(struct fanotify_event
> *event, char __user *buf)
>
>         buf += sizeof(handle);
>         len -= sizeof(handle);
> -       if (copy_to_user(buf, fanotify_event_fh(event), fh_len))
> +
> +       /*
> +        * For an inline fh, copy through stack to exclude the copy from
> +        * usercopy hardening protections.
> +        */
> +       fh = fanotify_event_fh(event);
> +       if (fh_len <= sizeof(bounce)) {

Prefer <= FANOTIFY_INLINE_FH_LEN

> +               memcpy(bounce, fh, fh_len);
> +               fh = bounce;
> +       }
> +
> +       if (copy_to_user(buf, fh, fh_len))
>                 return -EFAULT;
>
>         /* Pad with 0's */
>
>
> --
> Kees Cook

Re: WARNING: bad usercopy in fanotify_read

[Jan Kara]

On Tue 12-03-19 23:26:22, Kees Cook wrote:
> On Mon, Mar 11, 2019 at 1:42 PM syzbot
> <syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com> wrote:
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000
> > [...]
> > ------------[ cut here ]------------
> > Bad or missing usercopy whitelist? Kernel memory exposure attempt detected
> > from SLAB object 'fanotify_event' (offset 40, size 8)!
> > [...]
> >   copy_to_user include/linux/uaccess.h:151 [inline]
> >   copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
> >   copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]
> 
> Looks like this is the fh/ext_fh union in struct fanotify_fid, field
> "fid" in struct fanotify_event. Given that "fid" is itself in a union
> against a struct path, I think instead of a whitelist using
> KMEM_CACHE_USERCOPY(), this should just use a bounce buffer to avoid
> leaving a whitelist open for path or ext_fh exposure.

Do you mean to protect it from a situation when some other code (i.e. not
copy_fid_to_user()) would be tricked into copying ext_fh containing slab
pointer to userspace?

								Honza

> 
> Maybe something like this (untested):
> 
> diff --git a/fs/notify/fanotify/fanotify_user.c
> b/fs/notify/fanotify/fanotify_user.c
> index 56992b32c6bb..b87da9580b3c 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -207,6 +207,7 @@ static int process_access_response(struct
> fsnotify_group *group,
>  static int copy_fid_to_user(struct fanotify_event *event, char __user *buf)
>  {
>         struct fanotify_event_info_fid info = { };
> +       unsigned char bounce[FANOTIFY_INLINE_FH_LEN], *fh;
>         struct file_handle handle = { };
>         size_t fh_len = event->fh_len;
>         size_t len = fanotify_event_info_len(event);
> @@ -233,7 +234,18 @@ static int copy_fid_to_user(struct fanotify_event
> *event, char __user *buf)
> 
>         buf += sizeof(handle);
>         len -= sizeof(handle);
> -       if (copy_to_user(buf, fanotify_event_fh(event), fh_len))
> +
> +       /*
> +        * For an inline fh, copy through stack to exclude the copy from
> +        * usercopy hardening protections.
> +        */
> +       fh = fanotify_event_fh(event);
> +       if (fh_len <= sizeof(bounce)) {
> +               memcpy(bounce, fh, fh_len);
> +               fh = bounce;
> +       }
> +
> +       if (copy_to_user(buf, fh, fh_len))
>                 return -EFAULT;
> 
>         /* Pad with 0's */
> 
> 
> -- 
> Kees Cook
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: WARNING: bad usercopy in fanotify_read

[Kees Cook]

On Wed, Mar 13, 2019 at 7:35 AM Jan Kara <jack@suse.cz> wrote:
> On Tue 12-03-19 23:26:22, Kees Cook wrote:
> > On Mon, Mar 11, 2019 at 1:42 PM syzbot
> > <syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com> wrote:
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000
> > > [...]
> > > ------------[ cut here ]------------
> > > Bad or missing usercopy whitelist? Kernel memory exposure attempt detected
> > > from SLAB object 'fanotify_event' (offset 40, size 8)!
> > > [...]
> > >   copy_to_user include/linux/uaccess.h:151 [inline]
> > >   copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
> > >   copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]
> >
> > Looks like this is the fh/ext_fh union in struct fanotify_fid, field
> > "fid" in struct fanotify_event. Given that "fid" is itself in a union
> > against a struct path, I think instead of a whitelist using
> > KMEM_CACHE_USERCOPY(), this should just use a bounce buffer to avoid
> > leaving a whitelist open for path or ext_fh exposure.
>
> Do you mean to protect it from a situation when some other code (i.e. not
> copy_fid_to_user()) would be tricked into copying ext_fh containing slab
> pointer to userspace?

Yes. That's the design around the usercopy hardening. The
"whitelisting" is either via code (with a bounce buffer, so only the
specific "expected" code path can copy it), with a
kmem_create_usercopy() range marking (generally best for areas that
are not unions or when bounce buffers would be too big/slow), or with
implicit whitelisting (via a constant copy size that cannot change at
run-time, like: copy_to_user(dst, src, 6)).

In this case, since there are multiple unions in place and
FANOTIFY_INLINE_FH_LEN is small, it seemed best to go with a bounce
buffer.

-- 
Kees Cook

Re: WARNING: bad usercopy in fanotify_read

[Kees Cook]

On Wed, Mar 13, 2019 at 7:35 AM Jan Kara <jack@suse.cz> wrote:
> On Tue 12-03-19 23:26:22, Kees Cook wrote:
> > On Mon, Mar 11, 2019 at 1:42 PM syzbot
> > <syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com> wrote:
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000
> > > [...]
> > > ------------[ cut here ]------------
> > > Bad or missing usercopy whitelist? Kernel memory exposure attempt detected
> > > from SLAB object 'fanotify_event' (offset 40, size 8)!
> > > [...]
> > >   copy_to_user include/linux/uaccess.h:151 [inline]
> > >   copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
> > >   copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]
> >
> > Looks like this is the fh/ext_fh union in struct fanotify_fid, field
> > "fid" in struct fanotify_event. Given that "fid" is itself in a union
> > against a struct path, I think instead of a whitelist using
> > KMEM_CACHE_USERCOPY(), this should just use a bounce buffer to avoid
> > leaving a whitelist open for path or ext_fh exposure.
>
> Do you mean to protect it from a situation when some other code (i.e. not
> copy_fid_to_user()) would be tricked into copying ext_fh containing slab
> pointer to userspace?

Yes. That's the design around the usercopy hardening. The
"whitelisting" is either via code (with a bounce buffer, so only the
specific "expected" code path can copy it), with a
kmem_create_usercopy() range marking (generally best for areas that
are not unions or when bounce buffers would be too big/slow), or with
implicit whitelisting (via a constant copy size that cannot change at
run-time, like: copy_to_user(dst, src, 6)).

In this case, since there are multiple unions in place and
FANOTIFY_INLINE_FH_LEN is small, it seemed best to go with a bounce
buffer.

-- 
Kees Cook

Re: WARNING: bad usercopy in fanotify_read

[Jan Kara]

On Wed 13-03-19 08:35:33, Kees Cook wrote:
> On Wed, Mar 13, 2019 at 7:35 AM Jan Kara <jack@suse.cz> wrote:
> > On Tue 12-03-19 23:26:22, Kees Cook wrote:
> > > On Mon, Mar 11, 2019 at 1:42 PM syzbot
> > > <syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com> wrote:
> > > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000
> > > > [...]
> > > > ------------[ cut here ]------------
> > > > Bad or missing usercopy whitelist? Kernel memory exposure attempt detected
> > > > from SLAB object 'fanotify_event' (offset 40, size 8)!
> > > > [...]
> > > >   copy_to_user include/linux/uaccess.h:151 [inline]
> > > >   copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
> > > >   copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]
> > >
> > > Looks like this is the fh/ext_fh union in struct fanotify_fid, field
> > > "fid" in struct fanotify_event. Given that "fid" is itself in a union
> > > against a struct path, I think instead of a whitelist using
> > > KMEM_CACHE_USERCOPY(), this should just use a bounce buffer to avoid
> > > leaving a whitelist open for path or ext_fh exposure.
> >
> > Do you mean to protect it from a situation when some other code (i.e. not
> > copy_fid_to_user()) would be tricked into copying ext_fh containing slab
> > pointer to userspace?
> 
> Yes. That's the design around the usercopy hardening. The
> "whitelisting" is either via code (with a bounce buffer, so only the
> specific "expected" code path can copy it), with a
> kmem_create_usercopy() range marking (generally best for areas that
> are not unions or when bounce buffers would be too big/slow), or with
> implicit whitelisting (via a constant copy size that cannot change at
> run-time, like: copy_to_user(dst, src, 6)).
> 
> In this case, since there are multiple unions in place and
> FANOTIFY_INLINE_FH_LEN is small, it seemed best to go with a bounce
> buffer.

OK, makes sense. I'll replace tha patch using kmem_create_usercopy() in my
tree with a variant you've suggested.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: WARNING: bad usercopy in fanotify_read

[syzbot]

syzbot has bisected this bug to:

commit a8b13aa20afb69161b5123b4f1acc7ea0a03d360
Author: Amir Goldstein <amir73il@gmail.com>
Date:   Thu Jan 10 17:04:36 2019 +0000

     fanotify: enable FAN_REPORT_FID init flag

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11e78d6f200000
start commit:   a8b13aa2 fanotify: enable FAN_REPORT_FID init flag
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=13e78d6f200000
console output: https://syzkaller.appspot.com/x/log.txt?x=15e78d6f200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e9d91b7192a5e96e
dashboard link: https://syzkaller.appspot.com/bug?extid=2c49971e251e36216d1f
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1287516f200000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000

Reported-by: syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com
Fixes: a8b13aa2 ("fanotify: enable FAN_REPORT_FID init flag")

Re: WARNING: bad usercopy in fanotify_read

[syzbot]

syzbot has bisected this bug to:

commit a8b13aa20afb69161b5123b4f1acc7ea0a03d360
Author: Amir Goldstein <amir73il@gmail.com>
Date:   Thu Jan 10 17:04:36 2019 +0000

     fanotify: enable FAN_REPORT_FID init flag

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11e78d6f200000
start commit:   a8b13aa2 fanotify: enable FAN_REPORT_FID init flag
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=13e78d6f200000
console output: https://syzkaller.appspot.com/x/log.txt?x=15e78d6f200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e9d91b7192a5e96e
dashboard link: https://syzkaller.appspot.com/bug?extid=2c49971e251e36216d1f
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1287516f200000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000

Reported-by: syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com
Fixes: a8b13aa2 ("fanotify: enable FAN_REPORT_FID init flag")

Re: WARNING: bad usercopy in fanotify_read

[Kees Cook]

On Wed, Mar 13, 2019 at 8:47 AM Jan Kara <jack@suse.cz> wrote:
>
> On Wed 13-03-19 08:35:33, Kees Cook wrote:
> > On Wed, Mar 13, 2019 at 7:35 AM Jan Kara <jack@suse.cz> wrote:
> > > On Tue 12-03-19 23:26:22, Kees Cook wrote:
> > > > On Mon, Mar 11, 2019 at 1:42 PM syzbot
> > > > <syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com> wrote:
> > > > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000
> > > > > [...]
> > > > > ------------[ cut here ]------------
> > > > > Bad or missing usercopy whitelist? Kernel memory exposure attempt detected
> > > > > from SLAB object 'fanotify_event' (offset 40, size 8)!
> > > > > [...]
> > > > >   copy_to_user include/linux/uaccess.h:151 [inline]
> > > > >   copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
> > > > >   copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]
> > > >
> > > > Looks like this is the fh/ext_fh union in struct fanotify_fid, field
> > > > "fid" in struct fanotify_event. Given that "fid" is itself in a union
> > > > against a struct path, I think instead of a whitelist using
> > > > KMEM_CACHE_USERCOPY(), this should just use a bounce buffer to avoid
> > > > leaving a whitelist open for path or ext_fh exposure.
> > >
> > > Do you mean to protect it from a situation when some other code (i.e. not
> > > copy_fid_to_user()) would be tricked into copying ext_fh containing slab
> > > pointer to userspace?
> >
> > Yes. That's the design around the usercopy hardening. The
> > "whitelisting" is either via code (with a bounce buffer, so only the
> > specific "expected" code path can copy it), with a
> > kmem_create_usercopy() range marking (generally best for areas that
> > are not unions or when bounce buffers would be too big/slow), or with
> > implicit whitelisting (via a constant copy size that cannot change at
> > run-time, like: copy_to_user(dst, src, 6)).
> >
> > In this case, since there are multiple unions in place and
> > FANOTIFY_INLINE_FH_LEN is small, it seemed best to go with a bounce
> > buffer.
>
> OK, makes sense. I'll replace tha patch using kmem_create_usercopy() in my
> tree with a variant you've suggested.

Thanks! If you're able to update the patch, it would be nice to include:

Reported-by: syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com
Fixes: a8b13aa2 ("fanotify: enable FAN_REPORT_FID init flag")

Regardless, I'll flag the fix for syzbot:

#syz fix: fanotify: Allow copying of file handle to userspace

-- 
Kees Cook

Re: WARNING: bad usercopy in fanotify_read

[Kees Cook]

On Wed, Mar 13, 2019 at 8:47 AM Jan Kara <jack@suse.cz> wrote:
>
> On Wed 13-03-19 08:35:33, Kees Cook wrote:
> > On Wed, Mar 13, 2019 at 7:35 AM Jan Kara <jack@suse.cz> wrote:
> > > On Tue 12-03-19 23:26:22, Kees Cook wrote:
> > > > On Mon, Mar 11, 2019 at 1:42 PM syzbot
> > > > <syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com> wrote:
> > > > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000
> > > > > [...]
> > > > > ------------[ cut here ]------------
> > > > > Bad or missing usercopy whitelist? Kernel memory exposure attempt detected
> > > > > from SLAB object 'fanotify_event' (offset 40, size 8)!
> > > > > [...]
> > > > >   copy_to_user include/linux/uaccess.h:151 [inline]
> > > > >   copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
> > > > >   copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]
> > > >
> > > > Looks like this is the fh/ext_fh union in struct fanotify_fid, field
> > > > "fid" in struct fanotify_event. Given that "fid" is itself in a union
> > > > against a struct path, I think instead of a whitelist using
> > > > KMEM_CACHE_USERCOPY(), this should just use a bounce buffer to avoid
> > > > leaving a whitelist open for path or ext_fh exposure.
> > >
> > > Do you mean to protect it from a situation when some other code (i.e. not
> > > copy_fid_to_user()) would be tricked into copying ext_fh containing slab
> > > pointer to userspace?
> >
> > Yes. That's the design around the usercopy hardening. The
> > "whitelisting" is either via code (with a bounce buffer, so only the
> > specific "expected" code path can copy it), with a
> > kmem_create_usercopy() range marking (generally best for areas that
> > are not unions or when bounce buffers would be too big/slow), or with
> > implicit whitelisting (via a constant copy size that cannot change at
> > run-time, like: copy_to_user(dst, src, 6)).
> >
> > In this case, since there are multiple unions in place and
> > FANOTIFY_INLINE_FH_LEN is small, it seemed best to go with a bounce
> > buffer.
>
> OK, makes sense. I'll replace tha patch using kmem_create_usercopy() in my
> tree with a variant you've suggested.

Thanks! If you're able to update the patch, it would be nice to include:

Reported-by: syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com
Fixes: a8b13aa2 ("fanotify: enable FAN_REPORT_FID init flag")

Regardless, I'll flag the fix for syzbot:

#syz fix: fanotify: Allow copying of file handle to userspace

-- 
Kees Cook

Re: WARNING: bad usercopy in fanotify_read

[Jan Kara]

On Mon 18-03-19 11:27:12, Kees Cook wrote:
> On Wed, Mar 13, 2019 at 8:47 AM Jan Kara <jack@suse.cz> wrote:
> >
> > On Wed 13-03-19 08:35:33, Kees Cook wrote:
> > > On Wed, Mar 13, 2019 at 7:35 AM Jan Kara <jack@suse.cz> wrote:
> > > > On Tue 12-03-19 23:26:22, Kees Cook wrote:
> > > > > On Mon, Mar 11, 2019 at 1:42 PM syzbot
> > > > > <syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com> wrote:
> > > > > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000
> > > > > > [...]
> > > > > > ------------[ cut here ]------------
> > > > > > Bad or missing usercopy whitelist? Kernel memory exposure attempt detected
> > > > > > from SLAB object 'fanotify_event' (offset 40, size 8)!
> > > > > > [...]
> > > > > >   copy_to_user include/linux/uaccess.h:151 [inline]
> > > > > >   copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
> > > > > >   copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]
> > > > >
> > > > > Looks like this is the fh/ext_fh union in struct fanotify_fid, field
> > > > > "fid" in struct fanotify_event. Given that "fid" is itself in a union
> > > > > against a struct path, I think instead of a whitelist using
> > > > > KMEM_CACHE_USERCOPY(), this should just use a bounce buffer to avoid
> > > > > leaving a whitelist open for path or ext_fh exposure.
> > > >
> > > > Do you mean to protect it from a situation when some other code (i.e. not
> > > > copy_fid_to_user()) would be tricked into copying ext_fh containing slab
> > > > pointer to userspace?
> > >
> > > Yes. That's the design around the usercopy hardening. The
> > > "whitelisting" is either via code (with a bounce buffer, so only the
> > > specific "expected" code path can copy it), with a
> > > kmem_create_usercopy() range marking (generally best for areas that
> > > are not unions or when bounce buffers would be too big/slow), or with
> > > implicit whitelisting (via a constant copy size that cannot change at
> > > run-time, like: copy_to_user(dst, src, 6)).
> > >
> > > In this case, since there are multiple unions in place and
> > > FANOTIFY_INLINE_FH_LEN is small, it seemed best to go with a bounce
> > > buffer.
> >
> > OK, makes sense. I'll replace tha patch using kmem_create_usercopy() in my
> > tree with a variant you've suggested.
> 
> Thanks! If you're able to update the patch, it would be nice to include:
> 
> Reported-by: syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com
> Fixes: a8b13aa2 ("fanotify: enable FAN_REPORT_FID init flag")

Yeah, it's easy enough to amend the commit at this point. Done.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR