[PATCH AUTOSEL 5.10 03/15] fs/jfs: Prevent integer overflow in AG size calculation

Sasha Levin
2025-04-03T19:10:13Z

From: Rand Deeb <rand.sec96@gmail.com>

[ Upstream commit 7fcbf789629cdb9fbf4e2172ce31136cfed11e5e ]

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@gmail.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 389dafd23d15e..3cc10f9bf9f8b 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;
--
2.39.5