xfs: fix mount failure crash on invalid iclog memory access

BugLink: https://bugs.launchpad.net/bugs/1860602
[ Upstream commit 798a9cada4694ca8d970259f216cec47e675bfd5 ]

syzbot (via KASAN) reports a use-after-free in the error path of
xlog_alloc_log(). Specifically, the iclog freeing loop doesn't
handle the case of a fully initialized ->l_iclog linked list.
Instead, it assumes that the list is partially constructed and NULL
terminated.

This bug manifested because there was no possible error scenario
after iclog list setup when the original code was added.  Subsequent
code and associated error conditions were added some time later,
while the original error handling code was never updated. Fix up the
error loop to terminate either on a NULL iclog or reaching the end
of the list.

Reported-by: syzbot+c732f8644185de340492@syzkaller.appspotmail.com
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index a503af96d780ecf9fd15f6c6d579bc9822abac6f..2dde89fa1ffae48803a0dedbdc1af9576b147490 100644 (file)
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -1568,6 +1568,8 @@ out_free_iclog:
                if (iclog->ic_bp)
                        xfs_buf_free(iclog->ic_bp);
                kmem_free(iclog);
+               if (prev_iclog == log->l_iclog)
+                       break;
        }
        spinlock_destroy(&log->l_icloglock);
        xfs_buf_free(log->l_xbuf);