linux-kernel - [PATCH] ocfs2: mount fails with buffer overflow in strlen

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Message-Id: <20210927154459.15976-1-vvidic@valentin-vidic.from.hr>
Date:   Mon, 27 Sep 2021 17:44:59 +0200
From:   Valentin Vidic <vvidic@...entin-vidic.from.hr>
To:     Mark Fasheh <mark@...heh.com>, Joel Becker <jlbec@...lplan.org>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        ocfs2-devel@....oracle.com, linux-kernel@...r.kernel.org
Cc:     Valentin Vidic <vvidic@...entin-vidic.from.hr>
Subject: [PATCH] ocfs2: mount fails with buffer overflow in strlen

Starting with kernel v5.11 mouting an ocfs2 filesystem with either o2cb
or pcmk cluster stack fails with the trace below. Problem seems to be
that strings for cluster stack and cluster name are not guaranteed to be
null terminated in the disk representation, while strlcpy assumes that
the source string is always null terminated. This causes a read outside
of the source string triggering the buffer overflow detection.

detected buffer overflow in strlen
------------[ cut here ]------------
kernel BUG at lib/string.c:1149!
invalid opcode: 0000 [#1] SMP PTI
CPU: 1 PID: 910 Comm: mount.ocfs2 Not tainted 5.14.0-1-amd64 #1
  Debian 5.14.6-2
RIP: 0010:fortify_panic+0xf/0x11
...
Call Trace:
 ocfs2_initialize_super.isra.0.cold+0xc/0x18 [ocfs2]
 ocfs2_fill_super+0x359/0x19b0 [ocfs2]
 mount_bdev+0x185/0x1b0
 ? ocfs2_remount+0x440/0x440 [ocfs2]
 legacy_get_tree+0x27/0x40
 vfs_get_tree+0x25/0xb0
 path_mount+0x454/0xa20
 __x64_sys_mount+0x103/0x140
 do_syscall_64+0x3b/0xc0
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Signed-off-by: Valentin Vidic <vvidic@...entin-vidic.from.hr>
---
 fs/ocfs2/super.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
index c86bd4e60e20..1dea535224df 100644
--- a/fs/ocfs2/super.c
+++ b/fs/ocfs2/super.c
@@ -2169,9 +2169,10 @@ static int ocfs2_initialize_super(struct super_block *sb,
 	if (ocfs2_clusterinfo_valid(osb)) {
 		osb->osb_stackflags =
 			OCFS2_RAW_SB(di)->s_cluster_info.ci_stackflags;
-		strlcpy(osb->osb_cluster_stack,
+		memcpy(osb->osb_cluster_stack,
 		       OCFS2_RAW_SB(di)->s_cluster_info.ci_stack,
-		       OCFS2_STACK_LABEL_LEN + 1);
+		       OCFS2_STACK_LABEL_LEN);
+		osb->osb_cluster_stack[OCFS2_STACK_LABEL_LEN] = '\0';
 		if (strlen(osb->osb_cluster_stack) != OCFS2_STACK_LABEL_LEN) {
 			mlog(ML_ERROR,
 			     "couldn't mount because of an invalid "
@@ -2180,9 +2181,10 @@ static int ocfs2_initialize_super(struct super_block *sb,
 			status = -EINVAL;
 			goto bail;
 		}
-		strlcpy(osb->osb_cluster_name,
+		memcpy(osb->osb_cluster_name,
 			OCFS2_RAW_SB(di)->s_cluster_info.ci_cluster,
-			OCFS2_CLUSTER_NAME_LEN + 1);
+			OCFS2_CLUSTER_NAME_LEN);
+		osb->osb_cluster_name[OCFS2_CLUSTER_NAME_LEN] = '\0';
 	} else {
 		/* The empty string is identical with classic tools that
 		 * don't know about s_cluster_info. */
-- 
2.30.2