KASAN: null-ptr-deref Write in get_block

KASAN: null-ptr-deref Write in get_block

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    fb33c651 Linux 5.6-rc6
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=157d4b45e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9f894bd92023de02
dashboard link: https://syzkaller.appspot.com/bug?extid=4a88b2b9dc280f47baf4
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=127acd55e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15f82345e00000

Bisection is inconclusive: the bug happens on the oldest tested release.

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10e8d8d3e00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=12e8d8d3e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=14e8d8d3e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4a88b2b9dc280f47baf4@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in test_and_set_bit_lock include/asm-generic/bitops/instrumented-lock.h:55 [inline]
BUG: KASAN: null-ptr-deref in trylock_buffer include/linux/buffer_head.h:359 [inline]
BUG: KASAN: null-ptr-deref in lock_buffer include/linux/buffer_head.h:365 [inline]
BUG: KASAN: null-ptr-deref in alloc_branch fs/minix/itree_common.c:88 [inline]
BUG: KASAN: null-ptr-deref in get_block+0x657/0x1380 fs/minix/itree_common.c:191
Write of size 8 at addr 0000000000000000 by task syz-executor110/9537

CPU: 0 PID: 9537 Comm: syz-executor110 Not tainted 5.6.0-rc6-syzkaller #0
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+0x188/0x20d lib/dump_stack.c:118
 __kasan_report.cold+0x5/0x32 mm/kasan/report.c:510
 kasan_report+0xe/0x20 mm/kasan/common.c:641
 check_memory_region_inline mm/kasan/generic.c:185 [inline]
 check_memory_region+0x128/0x190 mm/kasan/generic.c:192
 test_and_set_bit_lock include/asm-generic/bitops/instrumented-lock.h:55 [inline]
 trylock_buffer include/linux/buffer_head.h:359 [inline]
 lock_buffer include/linux/buffer_head.h:365 [inline]
 alloc_branch fs/minix/itree_common.c:88 [inline]
 get_block+0x657/0x1380 fs/minix/itree_common.c:191
 minix_get_block+0xe5/0x110 fs/minix/inode.c:376
 __block_write_begin_int+0x490/0x1b00 fs/buffer.c:2008
 __block_write_begin fs/buffer.c:2058 [inline]
 block_write_begin+0x58/0x2e0 fs/buffer.c:2117
 minix_write_begin+0x35/0xe0 fs/minix/inode.c:412
 generic_perform_write+0x20a/0x4e0 mm/filemap.c:3287
 __generic_file_write_iter+0x24c/0x610 mm/filemap.c:3416
 generic_file_write_iter+0x3f0/0x62d mm/filemap.c:3448
 call_write_iter include/linux/fs.h:1902 [inline]
 new_sync_write+0x49c/0x700 fs/read_write.c:483
 __vfs_write+0xc9/0x100 fs/read_write.c:496
 vfs_write+0x262/0x5c0 fs/read_write.c:558
 ksys_write+0x127/0x250 fs/read_write.c:611
 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x44b389
Code: fd ca fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 cb ca fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f4e9f99ace8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00000000006ddc38 RCX: 000000000044b389
RDX: 000000000000fdef RSI: 00000000200004c0 RDI: 0000000000000005
RBP: 00000000006ddc30 R08: 0000000000000012 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006ddc3c
R13: 00007ffcd0e441ef R14: 00007f4e9f99b9c0 R15: 0000000000000001
==================================================================


---
This bug is generated by a bot. It may contain errors.
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

Re: KASAN: null-ptr-deref Write in get_block

[Qiujun Huang]

Need to check the return value of sb_getblk.

Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
---
 fs/minix/itree_common.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/minix/itree_common.c b/fs/minix/itree_common.c
index 043c3fd..eedd79f 100644
--- a/fs/minix/itree_common.c
+++ b/fs/minix/itree_common.c
@@ -85,6 +85,8 @@ static int alloc_branch(struct inode *inode,
  break;
  branch[n].key = cpu_to_block(nr);
  bh = sb_getblk(inode->i_sb, parent);
+ if (!bh)
+ break;
  lock_buffer(bh);
  memset(bh->b_data, 0, bh->b_size);
  branch[n].bh = bh;
--

Re: KASAN: null-ptr-deref Write in get_block

[Dan Carpenter]

Fix the subject to [PATCH] minix: Fix NULL dereference in alloc_branch()

On Sun, Mar 22, 2020 at 08:06:48PM +0800, Qiujun Huang wrote:
> Need to check the return value of sb_getblk.
> 

Add a Reported-by tag.

Reported-by: syzbot+4a88b2b9dc280f47baf4@syzkaller.appspotmail.com

> Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
> ---
>  fs/minix/itree_common.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/minix/itree_common.c b/fs/minix/itree_common.c
> index 043c3fd..eedd79f 100644
> --- a/fs/minix/itree_common.c
> +++ b/fs/minix/itree_common.c
> @@ -85,6 +85,8 @@ static int alloc_branch(struct inode *inode,
>   break;
>   branch[n].key = cpu_to_block(nr);
>   bh = sb_getblk(inode->i_sb, parent);
> + if (!bh)
> + break;

The patch is white space damaged and we need to do a bit of error
handling before the break as well.

 	bh = sb_getblk(inode->i_sb, parent);
+	if (!bh) {
+		minix_free_block(inode, block_to_cpu(branch[n].key));
+		break;
+	}
 	lock_buffer(bh);

Please fix those few things and resend.

regards,
dan carpenter

Re: KASAN: null-ptr-deref Write in get_block

[Qiujun Huang]

On Mon, Mar 23, 2020 at 7:42 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
>
> Fix the subject to [PATCH] minix: Fix NULL dereference in alloc_branch()
>
> On Sun, Mar 22, 2020 at 08:06:48PM +0800, Qiujun Huang wrote:
> > Need to check the return value of sb_getblk.
> >
>
> Add a Reported-by tag.
>
> Reported-by: syzbot+4a88b2b9dc280f47baf4@syzkaller.appspotmail.com
>
> > Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
> > ---
> >  fs/minix/itree_common.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/fs/minix/itree_common.c b/fs/minix/itree_common.c
> > index 043c3fd..eedd79f 100644
> > --- a/fs/minix/itree_common.c
> > +++ b/fs/minix/itree_common.c
> > @@ -85,6 +85,8 @@ static int alloc_branch(struct inode *inode,
> >   break;
> >   branch[n].key = cpu_to_block(nr);
> >   bh = sb_getblk(inode->i_sb, parent);
> > + if (!bh)
> > + break;
>
> The patch is white space damaged and we need to do a bit of error
> handling before the break as well.

I get it, thanks.

>
>         bh = sb_getblk(inode->i_sb, parent);
> +       if (!bh) {
> +               minix_free_block(inode, block_to_cpu(branch[n].key));
> +               break;
> +       }
>         lock_buffer(bh);
>
> Please fix those few things and resend.
>
> regards,
> dan carpenter
>