From: Al Viro viro@zeniv.linux.org.uk
[ Upstream commit 27cd1bf1240d482e4f02ca4f9812e748f3106e4f ]
incidentally, securityfs_recursive_remove() is broken without that - it leaks dentries, since simple_recursive_removal() does not expect anything of that sort. It could be worked around by dput() in remove_one() callback, but it's easier to just drop that double-get stuff.
Signed-off-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Sasha Levin sashal@kernel.org ---
LLM Generated explanations, may be completely bogus:
Now I have a clear understanding of the issue. Let me analyze this:
**YES**
This commit should be backported to stable kernel trees. Here's the extensive analysis:
## Analysis of the Double Dentry Reference Issue
The commit fixes a clear bug in securityfs where dentries are being pinned twice:
1. **The Bug**: In `securityfs_create_dentry()` at line 162, there's a `dget(dentry)` call immediately after `d_instantiate(dentry, inode)`. This creates an extra reference count on the dentry that is never properly balanced.
2. **Impact on `securityfs_remove()`**: The traditional `securityfs_remove()` function does call `dput(dentry)` at line 309, which would balance the extra `dget()`. However, this only happens for the simple remove case.
3. **Critical Impact on `securityfs_recursive_remove()`**: The newly added `securityfs_recursive_remove()` function (added in commit 7138679ff2a2) uses `simple_recursive_removal()` which expects normal dentry reference counting. The `simple_recursive_removal()` function in fs/libfs.c: - Takes its own reference with `dget(dentry)` at the beginning - Properly releases references with `dput()` calls throughout its execution - Does NOT expect the dentries to have extra references
4. **The Leak**: When `securityfs_recursive_remove()` is called, the extra reference from the `dget()` in `securityfs_create_dentry()` is never released because: - `simple_recursive_removal()` only releases the references it takes - The `remove_one()` callback only calls `simple_release_fs()` but doesn't do any `dput()` - This results in dentries being leaked with a refcount that never reaches zero
5. **Pattern Consistency**: Looking at similar filesystem implementations like debugfs (fs/debugfs/inode.c), they do NOT add an extra `dget()` after `d_instantiate()`. The pattern is simply: ```c d_instantiate(dentry, inode); return end_creating(dentry); ``` No extra reference is taken.
6. **Backport Criteria Met**: - **Fixes a real bug**: Memory leak of dentries when using `securityfs_recursive_remove()` - **Small and contained**: Single-line removal in two locations - **No side effects**: Removing the extra `dget()` brings the code in line with standard VFS patterns - **Low regression risk**: The fix makes securityfs consistent with other similar filesystems - **Important for stability**: Memory leaks in kernel filesystem code can accumulate over time
The commit message clearly identifies this as a bug fix ("securityfs_recursive_remove() is broken without that - it leaks dentries"), and the fix is minimal and correct. This makes it an ideal candidate for stable backporting.
security/inode.c | 2 -- 1 file changed, 2 deletions(-)
diff --git a/security/inode.c b/security/inode.c index 3aa75fffa8c9..a90b043695d9 100644 --- a/security/inode.c +++ b/security/inode.c @@ -159,7 +159,6 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode, inode->i_fop = fops; } d_instantiate(dentry, inode); - dget(dentry); inode_unlock(dir); return dentry;
@@ -306,7 +305,6 @@ void securityfs_remove(struct dentry *dentry) simple_rmdir(dir, dentry); else simple_unlink(dir, dentry); - dput(dentry); } inode_unlock(dir); simple_release_fs(&mount, &mount_count);