Re: [PATCH] jfs: add index corruption check to DT_GETPAGE()

[Dave Kleikamp]

On 2/26/25 2:25AM, Roman Smirnov wrote:
> If the file system is corrupted, the header.stblindex variable
> may become greater than 127. Because of this, an array access out
> of bounds may occur:
>
> ------------[ cut here ]------------
> UBSAN: array-index-out-of-bounds in fs/jfs/jfs_dtree.c:3096:10
> index 237 is out of range for type 'struct dtslot[128]'
> CPU: 0 UID: 0 PID: 5822 Comm: syz-executor740 Not tainted 6.13.0-rc4-syzkaller-00110-g4099a71718b0 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
> Call Trace:
>   <TASK>
>   __dump_stack lib/dump_stack.c:94 [inline]
>   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
>   ubsan_epilogue lib/ubsan.c:231 [inline]
>   __ubsan_handle_out_of_bounds+0x121/0x150 lib/ubsan.c:429
>   dtReadFirst+0x622/0xc50 fs/jfs/jfs_dtree.c:3096
>   dtReadNext fs/jfs/jfs_dtree.c:3147 [inline]
>   jfs_readdir+0x9aa/0x3c50 fs/jfs/jfs_dtree.c:2862
>   wrap_directory_iterator+0x91/0xd0 fs/readdir.c:65
>   iterate_dir+0x571/0x800 fs/readdir.c:108
>   __do_sys_getdents64 fs/readdir.c:403 [inline]
>   __se_sys_getdents64+0x1e2/0x4b0 fs/readdir.c:389
>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
>   </TASK>
> ---[ end trace ]---
>
> Add a stblindex check for corruption.

Looks reasonable. I'll pick this up.

Shaggy

> Reported-by: syzbot <syzbot+9120834fc227768625ba@xxxxxxxxxxxxxxxxxxxxxxxxx>
> Closes: https://syzkaller.appspot.com/bug?extid=9120834fc227768625ba
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Roman Smirnov <r.smirnov@xxxxxx>
> ---
>   fs/jfs/jfs_dtree.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/jfs/jfs_dtree.c b/fs/jfs/jfs_dtree.c
> index 8f85177f284b..93db6eec4465 100644
> --- a/fs/jfs/jfs_dtree.c
> +++ b/fs/jfs/jfs_dtree.c
> @@ -117,7 +117,8 @@ do {									\
>   	if (!(RC)) {							\
>   		if (((P)->header.nextindex >				\
>   		     (((BN) == 0) ? DTROOTMAXSLOT : (P)->header.maxslot)) || \
> -		    ((BN) && ((P)->header.maxslot > DTPAGEMAXSLOT))) {	\
> +		    ((BN) && (((P)->header.maxslot > DTPAGEMAXSLOT) ||	\
> +		    ((P)->header.stblindex >= DTPAGEMAXSLOT)))) {	\
>   			BT_PUTPAGE(MP);					\
>   			jfs_error((IP)->i_sb,				\
>   				  "DT_GETPAGE: dtree page corrupt\n");	\