diff options
| author | Al Viro <viro@zeniv.linux.org.uk> | 2023-11-20 20:02:11 -0500 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2023-11-25 02:54:14 -0500 |
| commit | a8b0026847b8c43445c921ad2c85521c92eb175f (patch) | |
| tree | 39078ede8594fab57ee0486e522655df86cb131f /fs/overlayfs/super.c | |
| parent | dbd4540df2b2857a91593754275c02f3e415fc30 (diff) | |
rename(): avoid a deadlock in the case of parents having no common ancestor
... and fix the directory locking documentation and proof of correctness.
Holding ->s_vfs_rename_mutex *almost* prevents ->d_parent changes; the
case where we really don't want it is splicing the root of disconnected
tree to somewhere.
In other words, ->s_vfs_rename_mutex is sufficient to stabilize "X is an
ancestor of Y" only if X and Y are already in the same tree. Otherwise
it can go from false to true, and one can construct a deadlock on that.
Make lock_two_directories() report an error in such case and update the
callers of lock_rename()/lock_rename_child() to handle such errors.
And yes, such conditions are not impossible to create ;-/
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/overlayfs/super.c')
| -rw-r--r-- | fs/overlayfs/super.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index a0967bb25003..fc3a6ff648bd 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -439,8 +439,10 @@ static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir) bool ok = false; if (workdir != upperdir) { - ok = (lock_rename(workdir, upperdir) == NULL); - unlock_rename(workdir, upperdir); + struct dentry *trap = lock_rename(workdir, upperdir); + if (!IS_ERR(trap)) + unlock_rename(workdir, upperdir); + ok = (trap == NULL); } return ok; } |