From c20e36b7631d83e7535877f08af8b0af72c44b1a Mon Sep 17 00:00:00 2001 From: Junrui Luo Date: Thu, 5 Mar 2026 20:05:48 +0800 Subject: [PATCH] dm log: fix out-of-bounds write due to region_count overflow 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 Signed-off-by: Junrui Luo Signed-off-by: Mikulas Patocka --- 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 1aa6a4a7d2323..d316757a328be 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) { -- 2.47.3