gfs2: Fix potential glock use-after-free on unmount

When a DLM lockspace is released and there ares still locks in that
lockspace, DLM will unlock those locks automatically.  Commit
fb6791d100d1b started exploiting this behavior to speed up filesystem
unmount: gfs2 would simply free glocks it didn't want to unlock and then
release the lockspace.  This didn't take the bast callbacks for
asynchronous lock contention notifications into account, which remain
active until until a lock is unlocked or its lockspace is released.

To prevent those callbacks from accessing deallocated objects, put the
glocks that should not be unlocked on the sd_dead_glocks list, release
the lockspace, and only then free those glocks.

As an additional measure, ignore unexpected ast and bast callbacks if
the receiving glock is dead.

Fixes: fb6791d100d1b ("GFS2: skip dlm_unlock calls in unmount")
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Cc: David Teigland <teigland@redhat.com>

1 files changed, 22 insertions, 10 deletions

diff --git a/fs/gfs2/lock_dlm.c b/fs/gfs2/lock_dlm.c
index d1ac5d0679ea..e028e55e67d9 100644
--- a/fs/gfs2/lock_dlm.c
+++ b/fs/gfs2/lock_dlm.c
@@ -121,6 +121,11 @@ static void gdlm_ast(void *arg)
 	struct gfs2_glock *gl = arg;
 	unsigned ret = gl->gl_state;
 
+	/* If the glock is dead, we only react to a dlm_unlock() reply. */
+	if (__lockref_is_dead(&gl->gl_lockref) &&
+	    gl->gl_lksb.sb_status != -DLM_EUNLOCK)
+		return;
+
 	gfs2_update_reply_times(gl);
 	BUG_ON(gl->gl_lksb.sb_flags & DLM_SBF_DEMOTED);
 
@@ -171,6 +176,9 @@ static void gdlm_bast(void *arg, int mode)
 {
 	struct gfs2_glock *gl = arg;
 
+	if (__lockref_is_dead(&gl->gl_lockref))
+		return;
+
 	switch (mode) {
 	case DLM_LOCK_EX:
 		gfs2_glock_cb(gl, LM_ST_UNLOCKED);
@@ -291,8 +299,12 @@ static void gdlm_put_lock(struct gfs2_glock *gl)
 	struct lm_lockstruct *ls = &sdp->sd_lockstruct;
 	int error;
 
-	if (gl->gl_lksb.sb_lkid == 0)
-		goto out_free;
+	BUG_ON(!__lockref_is_dead(&gl->gl_lockref));
+
+	if (gl->gl_lksb.sb_lkid == 0) {
+		gfs2_glock_free(gl);
+		return;
+	}
 
 	clear_bit(GLF_BLOCKING, &gl->gl_flags);
 	gfs2_glstats_inc(gl, GFS2_LKS_DCOUNT);
@@ -300,13 +312,17 @@ static void gdlm_put_lock(struct gfs2_glock *gl)
 	gfs2_update_request_times(gl);
 
 	/* don't want to call dlm if we've unmounted the lock protocol */
-	if (test_bit(DFL_UNMOUNT, &ls->ls_recover_flags))
-		goto out_free;
+	if (test_bit(DFL_UNMOUNT, &ls->ls_recover_flags)) {
+		gfs2_glock_free(gl);
+		return;
+	}
 	/* don't want to skip dlm_unlock writing the lvb when lock has one */
 
 	if (test_bit(SDF_SKIP_DLM_UNLOCK, &sdp->sd_flags) &&
-	    !gl->gl_lksb.sb_lvbptr)
-		goto out_free;
+	    !gl->gl_lksb.sb_lvbptr) {
+		gfs2_glock_free_later(gl);
+		return;
+	}
 
 again:
 	error = dlm_unlock(ls->ls_dlm, gl->gl_lksb.sb_lkid, DLM_LKF_VALBLK,
@@ -321,10 +337,6 @@ again:
 		       gl->gl_name.ln_type,
 		       (unsigned long long)gl->gl_name.ln_number, error);
 	}
-	return;
-
-out_free:
-	gfs2_glock_free(gl);
 }
 
 static void gdlm_cancel(struct gfs2_glock *gl)