* WARNING: bad usercopy in fanotify_read @ 2019-03-11 20:42 syzbot 2019-03-13 6:26 ` Kees Cook 2019-03-16 14:49 ` syzbot 0 siblings, 2 replies; 9+ messages in thread From: syzbot @ 2019-03-11 20:42 UTC (permalink / raw) To: akpm, cai, crecklin, keescook, linux-kernel, linux-mm, syzkaller-bugs 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 ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: WARNING: bad usercopy in fanotify_read 2019-03-11 20:42 WARNING: bad usercopy in fanotify_read syzbot @ 2019-03-13 6:26 ` Kees Cook 2019-03-13 6:42 ` Amir Goldstein 2019-03-13 14:35 ` Jan Kara 2019-03-16 14:49 ` syzbot 1 sibling, 2 replies; 9+ messages in thread From: Kees Cook @ 2019-03-13 6:26 UTC (permalink / raw) To: syzbot, Amir Goldstein, Jan Kara Cc: Andrew Morton, cai, Chris von Recklinghausen, LKML, Linux-MM, syzkaller-bugs 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 ^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: WARNING: bad usercopy in fanotify_read 2019-03-13 6:26 ` Kees Cook @ 2019-03-13 6:42 ` Amir Goldstein 2019-03-13 14:35 ` Jan Kara 1 sibling, 0 replies; 9+ messages in thread From: Amir Goldstein @ 2019-03-13 6:42 UTC (permalink / raw) To: Kees Cook Cc: syzbot, Jan Kara, Andrew Morton, cai, Chris von Recklinghausen, LKML, Linux-MM, syzkaller-bugs 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 ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: WARNING: bad usercopy in fanotify_read 2019-03-13 6:26 ` Kees Cook 2019-03-13 6:42 ` Amir Goldstein @ 2019-03-13 14:35 ` Jan Kara 2019-03-13 15:35 ` Kees Cook 1 sibling, 1 reply; 9+ messages in thread From: Jan Kara @ 2019-03-13 14:35 UTC (permalink / raw) To: Kees Cook Cc: syzbot, Amir Goldstein, Jan Kara, Andrew Morton, cai, Chris von Recklinghausen, LKML, Linux-MM, syzkaller-bugs 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 ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: WARNING: bad usercopy in fanotify_read 2019-03-13 14:35 ` Jan Kara @ 2019-03-13 15:35 ` Kees Cook 2019-03-13 15:47 ` Jan Kara 0 siblings, 1 reply; 9+ messages in thread From: Kees Cook @ 2019-03-13 15:35 UTC (permalink / raw) To: Jan Kara Cc: syzbot, Amir Goldstein, Andrew Morton, cai, Chris von Recklinghausen, LKML, Linux-MM, syzkaller-bugs 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 ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: WARNING: bad usercopy in fanotify_read 2019-03-13 15:35 ` Kees Cook @ 2019-03-13 15:47 ` Jan Kara 2019-03-18 18:27 ` Kees Cook 0 siblings, 1 reply; 9+ messages in thread From: Jan Kara @ 2019-03-13 15:47 UTC (permalink / raw) To: Kees Cook Cc: Jan Kara, syzbot, Amir Goldstein, Andrew Morton, cai, Chris von Recklinghausen, LKML, Linux-MM, syzkaller-bugs 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 ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: WARNING: bad usercopy in fanotify_read 2019-03-13 15:47 ` Jan Kara @ 2019-03-18 18:27 ` Kees Cook 2019-03-19 8:32 ` Jan Kara 0 siblings, 1 reply; 9+ messages in thread From: Kees Cook @ 2019-03-18 18:27 UTC (permalink / raw) To: Jan Kara Cc: syzbot, Amir Goldstein, Andrew Morton, cai, Chris von Recklinghausen, LKML, Linux-MM, syzkaller-bugs 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 ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: WARNING: bad usercopy in fanotify_read 2019-03-18 18:27 ` Kees Cook @ 2019-03-19 8:32 ` Jan Kara 0 siblings, 0 replies; 9+ messages in thread From: Jan Kara @ 2019-03-19 8:32 UTC (permalink / raw) To: Kees Cook Cc: Jan Kara, syzbot, Amir Goldstein, Andrew Morton, cai, Chris von Recklinghausen, LKML, Linux-MM, syzkaller-bugs 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 ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: WARNING: bad usercopy in fanotify_read 2019-03-11 20:42 WARNING: bad usercopy in fanotify_read syzbot 2019-03-13 6:26 ` Kees Cook @ 2019-03-16 14:49 ` syzbot 1 sibling, 0 replies; 9+ messages in thread From: syzbot @ 2019-03-16 14:49 UTC (permalink / raw) To: akpm, amir73il, cai, crecklin, jack, keescook, linux-api, linux-fsdevel, linux-kernel, linux-mm, syzkaller-bugs 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") ^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2019-03-19 8:32 UTC | newest] Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2019-03-11 20:42 WARNING: bad usercopy in fanotify_read syzbot 2019-03-13 6:26 ` Kees Cook 2019-03-13 6:42 ` Amir Goldstein 2019-03-13 14:35 ` Jan Kara 2019-03-13 15:35 ` Kees Cook 2019-03-13 15:47 ` Jan Kara 2019-03-18 18:27 ` Kees Cook 2019-03-19 8:32 ` Jan Kara 2019-03-16 14:49 ` syzbot
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