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.