Re: [PATCH v2] mm/vma: fix memory leak in __mmap_region()

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

On 3/31/26 20:08, Sechang Lim wrote:
> 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@kernel.org>
> Signed-off-by: Sechang Lim <rhkrqnwk98@gmail.com>

Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

Thanks!