[lvc-project] [PATCH] jfs: validate AG parameters in dbMount() to prevent crashes

[Dave Kleikamp]

Looks good. I'll put it through some tests and push it.

Thanks,
Shaggy

On 3/10/25 3:56AM, Vasiliy Kovalev wrote:
> Validate db_agheight, db_agwidth, and db_agstart in dbMount to catch
> corrupted metadata early and avoid undefined behavior in dbAllocAG.
> Limits are derived from L2LPERCTL, LPERCTL/MAXAG, and CTLTREESIZE:
> 
> - agheight: 0 to L2LPERCTL/2 (0 to 5) ensures shift
>    (L2LPERCTL - 2*agheight) >= 0.
> - agwidth: 1 to min(LPERCTL/MAXAG, 2^(L2LPERCTL - 2*agheight))
>    ensures agperlev >= 1.
>    - Ranges: 1-8 (agheight 0-3), 1-4 (agheight 4), 1 (agheight 5).
>    - LPERCTL/MAXAG = 1024/128 = 8 limits leaves per AG;
>      2^(10 - 2*agheight) prevents division to 0.
> - agstart: 0 to CTLTREESIZE-1 - agwidth*(MAXAG-1) keeps ti within
>    stree (size 1365).
>    - Ranges: 0-1237 (agwidth 1), 0-348 (agwidth 8).
> 
> UBSAN: shift-out-of-bounds in fs/jfs/jfs_dmap.c:1400:9
> shift exponent -335544310 is negative
> CPU: 0 UID: 0 PID: 5822 Comm: syz-executor130 Not tainted 6.14.0-rc5-syzkaller #0
> Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
> 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_shift_out_of_bounds+0x3c8/0x420 lib/ubsan.c:468
>   dbAllocAG+0x1087/0x10b0 fs/jfs/jfs_dmap.c:1400
>   dbDiscardAG+0x352/0xa20 fs/jfs/jfs_dmap.c:1613
>   jfs_ioc_trim+0x45a/0x6b0 fs/jfs/jfs_discard.c:105
>   jfs_ioctl+0x2cd/0x3e0 fs/jfs/ioctl.c:131
>   vfs_ioctl fs/ioctl.c:51 [inline]
>   __do_sys_ioctl fs/ioctl.c:906 [inline]
>   __se_sys_ioctl+0xf5/0x170 fs/ioctl.c:892
>   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
> 
> Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
> 
> Cc: stable at vger.kernel.org
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-by: syzbot+fe8264911355151c487f at syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=fe8264911355151c487f
> Signed-off-by: Vasiliy Kovalev <kovalev at altlinux.org>
> ---
>   fs/jfs/jfs_dmap.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
> index 26e89d0c69b61..cfb21f15f5971 100644
> --- a/fs/jfs/jfs_dmap.c
> +++ b/fs/jfs/jfs_dmap.c
> @@ -194,7 +194,11 @@ int dbMount(struct inode *ipbmap)
>   	    !bmp->db_numag || (bmp->db_numag > MAXAG) ||
>   	    (bmp->db_maxag >= MAXAG) || (bmp->db_maxag < 0) ||
>   	    (bmp->db_agpref >= MAXAG) || (bmp->db_agpref < 0) ||
> -	    !bmp->db_agwidth ||
> +	    bmp->db_agheight < 0 || bmp->db_agheight > (L2LPERCTL >> 1) ||
> +	    bmp->db_agwidth < 1 || bmp->db_agwidth > (LPERCTL / MAXAG) ||
> +	    bmp->db_agwidth > (1 << (L2LPERCTL - (bmp->db_agheight << 1))) ||
> +	    bmp->db_agstart < 0 || bmp->db_agstart >
> +	    (CTLTREESIZE - 1 - bmp->db_agwidth * (MAXAG - 1)) ||
>   	    (bmp->db_agl2size > L2MAXL2SIZE - L2MAXAG) ||
>   	    (bmp->db_agl2size < 0) ||
>   	    ((bmp->db_mapsize - 1) >> bmp->db_agl2size) > MAXAG) {