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[PATCH] btrfs: avoid null pointer dereference on fs_info when calling btrfs_crit

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  [PATCH] btrfs: avoid null pointer dereference on fs_info when calling btrfs_crit Colin King <colin.king@canonical.com> - 2017-09-11 17:20 +0200
    Re: [PATCH] btrfs: avoid null pointer dereference on fs_info when  calling btrfs_crit David Sterba <dsterba@suse.cz> - 2017-09-12 13:30 +0200

#1730390 — [PATCH] btrfs: avoid null pointer dereference on fs_info when calling btrfs_crit

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

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@canonical.com>
---
 fs/btrfs/super.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index e56a93f3113e..c669241f936e 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -202,7 +202,6 @@ static struct ratelimit_state printk_limits[] = {
 
 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_info *fs_info, const char *fmt, ...)
 	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);
 }
-- 
2.14.1

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#1730824 — Re: [PATCH] btrfs: avoid null pointer dereference on fs_info when calling btrfs_crit

On Mon, Sep 11, 2017 at 04:15:28PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> 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@canonical.com>

Reviewed-by: David Sterba <dsterba@suse.com>

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