In the Linux kernel, the following vulnerability has been resolved:
ocfs2: fix circular locking dependency in ocfs2_init_acl()
A lockdep warning indicates a circular locking dependency between
`&oi->ip_xattr_sem` and `&journal->j_trans_barrier`:
WARNING: possible circular locking dependency detected
is trying to acquire lock:
(&oi->ip_xattr_sem){++++}-{4:4}, at: ocfs2_init_acl+0x2fd/0x7e0
fs/ocfs2/acl.c:367
but task is already holding lock:
(&journal->j_trans_barrier){.+.+}-{4:4}, at: ocfs2_start_trans+0x3ab/0x700
fs/ocfs2/journal.c:369
The deadlock involves two code paths: Path 1 (setxattr) where
`ocfs2_xattr_set()` acquires `ip_xattr_sem` (write) and then starts a
transaction, which acquires `j_trans_barrier` (read); and Path 2
(mkdir/mknod) where `ocfs2_mknod()` starts a transaction (`j_trans_barrier`
read) and then calls `ocfs2_init_acl()`, which attempts to acquire
`ip_xattr_sem` (read) on the parent directory to retrieve the default ACL.
Because rw_semaphores are subject to writer priority, a pending writer on
`j_trans_barrier` (e.g., the journal commit thread) can cause Path 1 to
block, while Path 2 is blocked waiting for Path 1 to release
`ip_xattr_sem`.
The patch fixes the lock ordering by precomputing the ACL state before
starting the OCFS2 transaction, while preserving POSIX ACL storage
semantics and the existing inode/security initialization order. By reading
the parent directory’s default ACL and preparing the new inode’s ACLs
outside the transaction, `ip_xattr_sem` is always acquired before
`j_trans_barrier`.
`struct ocfs2_acl_state` encapsulates the prepared ACL state, while
`ocfs2_acl_init_prepare()` and `ocfs2_acl_init_release()` avoid code
duplication between `ocfs2_mknod()` and `ocfs2_init_security_and_acl()`.
`ocfs2_calc_xattr_init()` and `ocfs2_init_acl()` use this precomputed
state, removing internal `ip_xattr_sem` acquisition and redundant disk
reads.
Additionally, remove the `ip_xattr_sem` acquisition from
`ocfs2_xattr_set_handle()`. This function is only used while initializing a
new inode that has not yet been inserted into the inode hash or attached to
a dentry, meaning there is no risk of concurrent access and the lock is
unnecessary.
