在 2021/10/20 20:30, Greg KH 写道:

On Wed, Oct 13, 2021 at 06:49:06PM +0800, chenxiaosong (A) wrote:

quoted

在 2021/10/13 18:38, chenxiaosong (A) 写道:

quoted

在 2021/10/13 18:11, Greg KH 写道:

quoted

On Wed, Oct 13, 2021 at 05:51:01PM +0800, ChenXiaoSong wrote:

quoted

If two processes mount same superblock, memory leak occurs:

CPU0               |  CPU1
do_new_mount       |  do_new_mount
    fs_set_subtype   |    fs_set_subtype
      kstrdup        |
                     |      kstrdup
      memrory leak   |

Fix this by adding a write lock while calling fs_set_subtype.

Linus's tree already have refactoring patchset [1], one of them
can fix this bug:
          c30da2e981a7 (fuse: convert to use the new mount API)

Since we did not merge the refactoring patchset in this branch,
I create this patch.

[1] https://patchwork.kernel.org/project/linux-fsdevel/patch/20190903113640.7984-3-mszeredi@redhat.com/


Fixes: 79c0b2df79eb (add filesystem subtype support)
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: ChenXiaoSong <redacted>
---
v1: Can not mount sshfs ([PATCH linux-4.19.y] VFS: Fix fuseblk
memory leak caused by mount concurrency)
v2: Use write lock while writing superblock

   fs/namespace.c | 9 ++++++---
   1 file changed, 6 insertions(+), 3 deletions(-)

As you are referring to a fuse-only patch above, why are you trying to
resolve this issue in the core namespace code instead?

How does fuse have anything to do with this?

confused,

greg k-h
.

Now, only `fuse_fs_type` and `fuseblk_fs_type` has `FS_HAS_SUBTYPE` flag
in kernel code, but maybe there is a filesystem module(`struct
file_system_type` has `FS_HAS_SUBTYPE` flag). And only mounting fuseblk
filesystem(e.g. ntfs) will occur memory leak now.

How about updating the subject as: VFS: Fix memory leak caused by mounting
fs with subtype concurrency?

That would be a better idea, but still, this is not obvious that this is
the correct fix at all...
.

Why is this patch not correct? Can you tell me more about it? Thanks.