The local variable region_count in create_log_context() is declared as
unsigned int (32-bit), but dm_sector_div_up() returns sector_t (64-bit).
When a device-mapper target has a sufficiently large ti->len with a small
region_size, the division result can exceed UINT_MAX. The truncated
value is then used to calculate bitset_size, causing clean_bits,
sync_bits, and recovering_bits to be allocated far smaller than needed
for the actual number of regions.
Subsequent log operations (log_set_bit, log_clear_bit, log_test_bit) use
region indices derived from the full untruncated region space, causing
out-of-bounds writes to kernel heap memory allocated by vmalloc.
This can be reproduced by creating a mirror target whose region_count
overflows 32 bits:
dmsetup create bigzero --table '0 8589934594 zero'
dmsetup create mymirror --table '0 8589934594 mirror \
core 2 2 nosync 2 /dev/mapper/bigzero 0 \
/dev/mapper/bigzero 0'
The status output confirms the truncation (sync_count=1 instead of
4294967297, because 0x100000001 was truncated to 1):
$ dmsetup status mymirror
0 8589934594 mirror 2 254:1 254:1 1/4294967297 ...
This leads to a kernel crash in core_in_sync:
BUG: scheduling while atomic: (udev-worker)/9150/0x00000000
RIP: 0010:core_in_sync+0x14/0x30 [dm_log]
CR2: 0000000000000008
Fixing recursive fault but reboot is needed!
Fix by widening the local region_count to sector_t and adding an
explicit overflow check before the value is assigned to lc->region_count.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Yuhao Jiang <[email protected]>
Signed-off-by: Junrui Luo <[email protected]>
---
drivers/md/dm-log.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/md/dm-log.c b/drivers/md/dm-log.c
index 1aa6a4a7d232..d316757a328b 100644
--- a/drivers/md/dm-log.c
+++ b/drivers/md/dm-log.c
@@ -373,7 +373,7 @@ static int create_log_context(struct dm_dirty_log *log,
struct dm_target *ti,
struct log_c *lc;
uint32_t region_size;
- unsigned int region_count;
+ sector_t region_count;
size_t bitset_size, buf_size;
int r;
char dummy;
@@ -401,6 +401,10 @@ static int create_log_context(struct dm_dirty_log *log,
struct dm_target *ti,
}
region_count = dm_sector_div_up(ti->len, region_size);
+ if (region_count > UINT_MAX) {
+ DMWARN("region count exceeds limit of %u", UINT_MAX);
+ return -EINVAL;
+ }
lc = kmalloc_obj(*lc);
if (!lc) {
---
base-commit: 0031c06807cfa8aa51a759ff8aa09e1aa48149af
change-id: 20260305-fixes-156b89003e60
Best regards,
--
Junrui Luo <[email protected]>
