linux-kernel - [PATCH] mm/mmap: Fix memory leak in mmap

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Date:   Thu, 27 Oct 2022 10:58:37 +0800
From:   Li Zetao <lizetao1@...wei.com>
To:     <akpm@...ux-foundation.org>, <Liam.Howlett@...cle.com>,
        <willy@...radead.org>, <catalin.marinas@....com>
CC:     <lizetao@...wei.com>, <mike.kravetz@...cle.com>,
        <cmllamas@...gle.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, Li Zetao <lizetao1@...wei.com>
Subject: [PATCH] mm/mmap: Fix memory leak in mmap_region()

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().

Fixes: d4af56c5c7c6 ("mm: start tracking VMAs with maple tree")
Fixes: c462ac288f2c ("mm: Introduce arch_validate_flags()")
Signed-off-by: Li Zetao <lizetao1@...wei.com>
---
 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;
 	}
@@ -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)
 		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