ocfs2: fix missing metadata reservation for large xattrs

commit 0cdc7dd upstream.

[BUG]
lsetxattr() panics the kernel when setting a large xattr value on a
fragmented filesystem where the file already has an external xattr
block.

[CAUSE]
ocfs2_calc_xattr_set_need() never reserves metadata blocks for a new
xattr value's extent tree when the file already has an external xattr
block. The not_found path leaves meta_add at zero, so meta_ac is NULL
when ocfs2_xattr_extend_allocation() runs.

A new value root has room for a single extent record. On a fragmented
filesystem, the allocator cannot satisfy the xattr value in one
contiguous run, so each non-contiguous run requires its own extent
record. When the value root's extent list is full and meta_ac is NULL,
ocfs2_add_clusters_in_btree() returns RESTART_META, and
ocfs2_xattr_extend_allocation() hits BUG_ON(why == RESTART_META).

[FIX]
The case where no xattr block exists yet already calls
ocfs2_extend_meta_needed(&def_xv.xv.xr_list) to reserve value tree
metadata. Add the same reservation to the case where an xattr block
already exists, making the two cases consistent.

Replace the BUG_ON with a -ENOSPC return so that if RESTART_META is
returned despite the reservation, the error propagates to userspace
instead of panicking the kernel.

Link: https://lore.kernel.org/amLwn3i9tET8yhG7@dev
Fixes: a78f9f4 ("ocfs2: make xattr extension work with new local alloc reservation.")
Signed-off-by: Ian Bridges <icb@fastmail.org>
Reported-by: syzbot+e538032956b1157914a3@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=e538032956b1157914a3
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Cc: Heming Zhao <heming.zhao@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: icb-linux

fs/ocfs2/xattr.c

@@ -740,12 +740,10 @@ static int ocfs2_xattr_extend_allocation(struct inode *inode,
 					 prev_clusters;
 
 		if (why != RESTART_NONE && clusters_to_add) {
-			/*
-			 * We can only fail in case the alloc file doesn't give
-			 * up enough clusters.
-			 */
-			BUG_ON(why == RESTART_META);
-
+			if (why == RESTART_META) {
+				status = -ENOSPC;
+				break;
+			}
 			credits = ocfs2_calc_extend_credits(inode->i_sb,
 							    &vb->vb_xv->xr_list);
 			status = ocfs2_extend_trans(handle, credits);
@@ -3214,6 +3212,14 @@ static int ocfs2_calc_xattr_set_need(struct inode *inode,
 		} else
 			credits += OCFS2_SUBALLOC_ALLOC + 1;
 
+		/*
+		 * Reserve metadata for the new xattr's value extent tree.
+		 * The not_found path above adds credits for this tree but
+		 * omits meta_add, leaving meta_ac NULL for large values.
+		 */
+		if (xi->xi_value_len > OCFS2_XATTR_INLINE_SIZE)
+			meta_add += ocfs2_extend_meta_needed(&def_xv.xv.xr_list);
+
 		/*
 		 * This cluster will be used either for new bucket or for
 		 * new xattr block.