linux-ext4 - [PATCH 3/7] e2fsprogs: fix unexpected NULL variable

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Message-Id: <20210806095820.83731-3-lczerner@redhat.com>
Date:   Fri,  6 Aug 2021 11:58:16 +0200
From:   Lukas Czerner <lczerner@...hat.com>
To:     tytso@....edu
Cc:     linux-ext4@...r.kernel.org
Subject: [PATCH 3/7] e2fsprogs: fix unexpected NULL variable

The ext2fs_check_mount_point() function can be called with mtpt being
NULL as for example from ext2fs_check_if_mounted(). However in the
is_swap_device condition we use the mtpt in strncpy without checking
whether it is non-null first.

This should not be a problem on linux since the previous attempt to open
the device exclusively would have prevented us from ever reaching the
problematic strncpy. However it's still a bug and can cause problems on
other systems, fix it by conditioning strncpy on mtpt not being null.

Signed-off-by: Lukas Czerner <lczerner@...hat.com>
---
 lib/ext2fs/ismounted.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/ext2fs/ismounted.c b/lib/ext2fs/ismounted.c
index c9e6a9d0..aee7d726 100644
--- a/lib/ext2fs/ismounted.c
+++ b/lib/ext2fs/ismounted.c
@@ -393,7 +393,8 @@ errcode_t ext2fs_check_mount_point(const char *device, int *mount_flags,

 	if (is_swap_device(device)) {
 		*mount_flags = EXT2_MF_MOUNTED | EXT2_MF_SWAP;
-		strncpy(mtpt, "<swap>", mtlen);
+		if (mtpt)
+			strncpy(mtpt, "<swap>", mtlen);
 	} else {
 #ifdef HAVE_SETMNTENT
 		retval = check_mntent(device, mount_flags, mtpt, mtlen);
-- 
2.31.1