* Li Zetao <lizetao1@xxxxxxxxxx> [221026 21:55]:
> There is a memory leak reported by kmemleak:
>
> unreferenced object 0xffff88817231ce40 (size 224):
> comm "mount.cifs", pid 19308, jiffies 4295917571 (age 405.880s)
> hex dump (first 32 bytes):
> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> 60 c0 b2 00 81 88 ff ff 98 83 01 42 81 88 ff ff `..........B....
> backtrace:
> [<ffffffff81936171>] __alloc_file+0x21/0x250
> [<ffffffff81937051>] alloc_empty_file+0x41/0xf0
> [<ffffffff81937159>] alloc_file+0x59/0x710
> [<ffffffff81937964>] alloc_file_pseudo+0x154/0x210
> [<ffffffff81741dbf>] __shmem_file_setup+0xff/0x2a0
> [<ffffffff817502cd>] shmem_zero_setup+0x8d/0x160
> [<ffffffff817cc1d5>] mmap_region+0x1075/0x19d0
> [<ffffffff817cd257>] do_mmap+0x727/0x1110
> [<ffffffff817518b2>] vm_mmap_pgoff+0x112/0x1e0
> [<ffffffff83adf955>] do_syscall_64+0x35/0x80
> [<ffffffff83c0006a>] entry_SYSCALL_64_after_hwframe+0x46/0xb0
>
> The root cause was traced to an error handing path in mmap_region()
> when arch_validate_flags() or mas_preallocate() fails. In the shared
> anonymous mapping sence, vma will be setuped and mapped with a new
> shared anonymous file via shmem_zero_setup(). So in this case, the
> file resource needs to be released.
>
> Fix it by calling fput(vma->vm_file) when arch_validate_flags() or
> mas_preallocate() returns an error. And for the beauty of the code,
> put fput() under mapping_unmap_writable().
It does look like the unrolling is in the wrong order in that section.
>
> Fixes: d4af56c5c7c6 ("mm: start tracking VMAs with maple tree")
> Fixes: c462ac288f2c ("mm: Introduce arch_validate_flags()")
> Signed-off-by: Li Zetao <lizetao1@xxxxxxxxxx>
> ---
> mm/mmap.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index e270057ed04e..8530195b3ec5 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2674,6 +2674,8 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> error = -EINVAL;
> if (file)
> goto close_and_free_vma;
> + else if (vm_flags & VM_SHARED)
> + goto put_vma_file;
> else
> goto free_vma;
> }
> @@ -2682,6 +2684,8 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> error = -ENOMEM;
> if (file)
> goto close_and_free_vma;
> + else if (vm_flags & VM_SHARED)
> + goto put_vma_file;
> else
> goto free_vma;
> }
I am not happy about this getting more complex as it already duplicates
too much code.
> @@ -2746,13 +2750,13 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> if (vma->vm_ops && vma->vm_ops->close)
> vma->vm_ops->close(vma);
> unmap_and_free_vma:
> - fput(vma->vm_file);
> - vma->vm_file = NULL;
> -
> /* Undo any partial mapping done by a device driver. */
> unmap_region(mm, mas.tree, vma, prev, next, vma->vm_start, vma->vm_end);
> if (vm_flags & VM_SHARED)
Could we change the above if to "if (file && vm_flags & VM_SHARED)" and
jump to unmap_and_free_vma "if (vma->vm_file)"? We could then drop your
new goto label. I still think the reodering is correct and worth while.
Or am I missing something?
> mapping_unmap_writable(file->f_mapping);
> +put_vma_file:
> + fput(vma->vm_file);
> + vma->vm_file = NULL;
> free_vma:
> vm_area_free(vma);
> unacct_error:
> --
> 2.31.1
>
