linux-ext4 - [PATCH 21/74] e4defrag: don't crash if umounts the filesystem races with us

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Date:	Tue, 10 Dec 2013 17:20:40 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	tytso@....edu, darrick.wong@...cle.com
Cc:	linux-ext4@...r.kernel.org
Subject: [PATCH 21/74] e4defrag: don't crash if umounts the filesystem races
 with us

If someone umounts the filesystem between statfs64 and the getmntent()
iteration, we can exit the loop having never set mnt_type, and strcmp
can crash.  Fix the potential NULL deref.

Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
---
 misc/e4defrag.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/misc/e4defrag.c b/misc/e4defrag.c
index 4b31d03..b6e2e31 100644
--- a/misc/e4defrag.c
+++ b/misc/e4defrag.c
@@ -374,7 +374,7 @@ static int is_ext4(const char *file, char *devname)
 	}

 	endmntent(fp);
-	if (strcmp(mnt_type, FS_EXT4) == 0) {
+	if (mnt_type && strcmp(mnt_type, FS_EXT4) == 0) {
 		FREE(mnt_type);
 		return 0;
 	} else {

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