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@xxxxxxxxxx/
Fixes: 79c0b2df79eb (add filesystem subtype support)
Cc: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: ChenXiaoSong <chenxiaosong2@xxxxxxxxxx>
---
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(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index 2f3c6a0350a8..396ff1bcfdad 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2490,9 +2490,12 @@ static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
return -ENODEV;
mnt = vfs_kern_mount(type, sb_flags, name, data);
- if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
- !mnt->mnt_sb->s_subtype)
- mnt = fs_set_subtype(mnt, fstype);
+ if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE)) {
+ down_write(&mnt->mnt_sb->s_umount);
+ if (!mnt->mnt_sb->s_subtype)
+ mnt = fs_set_subtype(mnt, fstype);
+ up_write(&mnt->mnt_sb->s_umount);
+ }
put_filesystem(type);
if (IS_ERR(mnt))
--
2.25.4
