[PATCH v2] mm/vma: fix memory leak in __mmap_region()
From: Sechang Lim
Date: Tue Mar 31 2026 - 14:14:41 EST
commit 605f6586ecf7 ("mm/vma: do not leak memory when .mmap_prepare
swaps the file") handled the success path by skipping get_file() via
file_doesnt_need_get, but missed the error path.
When /dev/zero is mmap'd with MAP_SHARED, mmap_zero_prepare() calls
shmem_zero_setup_desc() which allocates a new shmem file to back the
mapping. If __mmap_new_vma() subsequently fails, this replacement
file is never fput()'d - the original is released by
ksys_mmap_pgoff(), but nobody releases the new one.
Add fput() for the swapped file in the error path.
Reproducible with fault injection.
FAULT_INJECTION: forcing a failure.
name failslab, interval 1, probability 0, space 0, times 1
CPU: 2 UID: 0 PID: 366 Comm: syz.7.14 Not tainted 7.0.0-rc6 #2 PREEMPT(full)
Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x164/0x1f0
should_fail_ex+0x525/0x650
should_failslab+0xdf/0x140
kmem_cache_alloc_noprof+0x78/0x630
vm_area_alloc+0x24/0x160
__mmap_region+0xf6b/0x2660
mmap_region+0x2eb/0x3a0
do_mmap+0xc79/0x1240
vm_mmap_pgoff+0x252/0x4c0
ksys_mmap_pgoff+0xf8/0x120
__x64_sys_mmap+0x12a/0x190
do_syscall_64+0xa9/0x580
entry_SYSCALL_64_after_hwframe+0x76/0x7e
</TASK>
kmemleak: 1 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
BUG: memory leak
unreferenced object 0xffff8881118aca80 (size 360):
comm "syz.7.14", pid 366, jiffies 4294913255
hex dump (first 32 bytes):
00 00 00 00 ad 4e ad de ff ff ff ff 00 00 00 00 .....N..........
ff ff ff ff ff ff ff ff c0 28 4d ae ff ff ff ff .........(M.....
backtrace (crc db0f53bc):
kmem_cache_alloc_noprof+0x3ab/0x630
alloc_empty_file+0x5a/0x1e0
alloc_file_pseudo+0x135/0x220
__shmem_file_setup+0x274/0x420
shmem_zero_setup_desc+0x9c/0x170
mmap_zero_prepare+0x123/0x140
__mmap_region+0xdda/0x2660
mmap_region+0x2eb/0x3a0
do_mmap+0xc79/0x1240
vm_mmap_pgoff+0x252/0x4c0
ksys_mmap_pgoff+0xf8/0x120
__x64_sys_mmap+0x12a/0x190
do_syscall_64+0xa9/0x580
entry_SYSCALL_64_after_hwframe+0x76/0x7e
Found by syzkaller.
Fixes: 605f6586ecf7 ("mm/vma: do not leak memory when .mmap_prepare swaps the file")
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@xxxxxxxxxx>
Signed-off-by: Sechang Lim <rhkrqnwk98@xxxxxxxxx>
-------
v2:
- Drop redundant map.file NULL check (Lorenzo)
- Add comment explaining the fput() (Lorenzo)
v1: https://lore.kernel.org/linux-mm/20260331121906.1301155-1-rhkrqnwk98@xxxxxxxxx/
mm/vma.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/mm/vma.c b/mm/vma.c
index be64f781a3aa..c8df5f561ad7 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -2781,6 +2781,13 @@ static unsigned long __mmap_region(struct file *file, unsigned long addr,
if (map.charged)
vm_unacct_memory(map.charged);
abort_munmap:
+ /*
+ * This indicates that .mmap_prepare has set a new file, differing from
+ * desc->vm_file. But since we're aborting the operation, only the
+ * original file will be cleaned up. Ensure we clean up both.
+ */
+ if (map.file_doesnt_need_get)
+ fput(map.file);
vms_abort_munmap_vmas(&map.vms, &map.mas_detach);
return error;
}
--
2.43.0