linux-kernel - [PATCH 4.14 111/178] btrfs: avoid null pointer dereference on fs_info when calling btrfs

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Message-Id: <20171218152925.328781099@linuxfoundation.org>
Date:   Mon, 18 Dec 2017 16:49:07 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Colin Ian King <colin.king@...onical.com>,
        David Sterba <dsterba@...e.com>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: [PATCH 4.14 111/178] btrfs: avoid null pointer dereference on fs_info when calling btrfs_crit

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Colin Ian King <colin.king@...onical.com>


[ Upstream commit 3993b112dac968612b0b213ed59cb30f50b0015b ]

There are checks on fs_info in __btrfs_panic to avoid dereferencing a
null fs_info, however, there is a call to btrfs_crit that may also
dereference a null fs_info. Fix this by adding a check to see if fs_info
is null and only print the s_id if fs_info is non-null.

Detected by CoverityScan CID#401973 ("Dereference after null check")

Fixes: efe120a067c8 ("Btrfs: convert printk to btrfs_ and fix BTRFS prefix")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
Reviewed-by: David Sterba <dsterba@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/btrfs/super.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -202,7 +202,6 @@ static struct ratelimit_state printk_lim
 
 void btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt, ...)
 {
-	struct super_block *sb = fs_info->sb;
 	char lvl[PRINTK_MAX_SINGLE_HEADER_LEN + 1] = "\0";
 	struct va_format vaf;
 	va_list args;
@@ -228,7 +227,8 @@ void btrfs_printk(const struct btrfs_fs_
 	vaf.va = &args;
 
 	if (__ratelimit(ratelimit))
-		printk("%sBTRFS %s (device %s): %pV\n", lvl, type, sb->s_id, &vaf);
+		printk("%sBTRFS %s (device %s): %pV\n", lvl, type,
+			fs_info ? fs_info->sb->s_id : "<unknown>", &vaf);
 
 	va_end(args);
 }