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| 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/util.c | |
| parent | dbd4540df2b2857a91593754275c02f3e415fc30 (diff) | |
| download | linux-stable-a8b0026847b8c43445c921ad2c85521c92eb175f.tar.gz linux-stable-a8b0026847b8c43445c921ad2c85521c92eb175f.tar.bz2 linux-stable-a8b0026847b8c43445c921ad2c85521c92eb175f.zip | |
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/util.c')
| -rw-r--r-- | fs/overlayfs/util.c | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c index 50a201e9cd39..7b667345e673 100644 --- a/fs/overlayfs/util.c +++ b/fs/overlayfs/util.c @@ -1198,12 +1198,17 @@ void ovl_nlink_end(struct dentry *dentry) int ovl_lock_rename_workdir(struct dentry *workdir, struct dentry *upperdir) { + struct dentry *trap; + /* Workdir should not be the same as upperdir */ if (workdir == upperdir) goto err; /* Workdir should not be subdir of upperdir and vice versa */ - if (lock_rename(workdir, upperdir) != NULL) + trap = lock_rename(workdir, upperdir); + if (IS_ERR(trap)) + goto err; + if (trap) goto err_unlock; return 0; |