Re: [PATCH 5.10.y] fs/jfs: Prevent integer overflow in AG size calculation

[Fedor Pchelkin]

On Tue, 18. Feb 15:44, Rand Deeb wrote:
> The JFS filesystem calculates allocation group (AG) size using 1 << 
> l2agsize in dbExtendFS(). When l2agsize exceeds 31 (possible with >2TB 
> aggregates on 32-bit systems), this 32-bit shift operation causes undefined
> behavior and improper AG sizing.
> 
> On 32-bit architectures:
> - Left-shifting 1 by 32+ bits results in 0 due to integer overflow
> - This creates invalid AG sizes (0 or garbage values) in 
> sbi->bmap->db_agsize
> - Subsequent block allocations would reference invalid AG structures
> - Could lead to: 
>   - Filesystem corruption during extend operations
>   - Kernel crashes due to invalid memory accesses
>   - Security vulnerabilities via malformed on-disk structures
> 
> Fix by casting to s64 before shifting:
> bmp->db_agsize = (s64)1 << l2agsize;
> 
> This ensures 64-bit arithmetic even on 32-bit architectures. The cast 
> matches the data type of db_agsize (s64) and follows similar patterns in 
> JFS block calculation code.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Signed-off-by: Rand Deeb <rand.sec96@xxxxxxxxx>
> ---

Same here. The patch is supposed to address the issue in the mainline
first.. What is the reason for '5.10.y' in the subject?

>  fs/jfs/jfs_dmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
> index ef220709c7f5..eedea23d70ff 100644
> --- a/fs/jfs/jfs_dmap.c
> +++ b/fs/jfs/jfs_dmap.c
> @@ -3465,7 +3465,7 @@ int dbExtendFS(struct inode *ipbmap, s64 blkno,	s64 nblocks)
>  	oldl2agsize = bmp->db_agl2size;
>  
>  	bmp->db_agl2size = l2agsize;
> -	bmp->db_agsize = 1 << l2agsize;
> +	bmp->db_agsize = (s64)1 << l2agsize;
>  
>  	/* compute new number of AG */
>  	agno = bmp->db_numag;
> -- 
> 2.34.1