[v2,14/21] kpartx: open /dev/loop-control only once

Commit Message

Martin Wilck Dec. 1, 2021, 12:36 p.m. UTC

From: Martin Wilck <[e-mail]>

Opening the same file repeatedly in a loop seems wrong.

For unknown reason, this patch caused gcc to diagnose a possible buffer
overflow for the device name, and I had to increase the buffer by
one byte.

Reviewed-by: Benjamin Marzinski <[e-mail]>
Signed-off-by: Martin Wilck <[e-mail]>
---
 kpartx/lopart.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

Patch

diff --git a/kpartx/lopart.c b/kpartx/lopart.c
index 9b65255..2661940 100644
--- a/kpartx/lopart.c
+++ b/kpartx/lopart.c
@@ -159,26 +159,28 @@  char *find_loop_by_file(const char *filename)
 
 char *find_unused_loop_device(void)
 {
-	char dev[20], *next_loop_dev = NULL;
+	char dev[21], *next_loop_dev = NULL;
 	int fd, next_loop = 0, somedev = 0, someloop = 0, loop_known = 0;
+	int next_loop_fd;
 	struct stat statbuf;
 	struct loop_info loopinfo;
 	FILE *procdev;
 
+	next_loop_fd = open("/dev/loop-control", O_RDWR);
+	if (next_loop_fd < 0)
+		return NULL;
+
+	if (!(fstat(next_loop_fd, &statbuf) == 0 && S_ISCHR(statbuf.st_mode))) {
+		close(next_loop_fd);
+		return NULL;
+	}
+
 	while (next_loop_dev == NULL) {
-		if (stat("/dev/loop-control", &statbuf) == 0 &&
-		    S_ISCHR(statbuf.st_mode)) {
-			int next_loop_fd;
-
-			next_loop_fd = open("/dev/loop-control", O_RDWR);
-			if (next_loop_fd < 0)
-				return NULL;
-			next_loop = ioctl(next_loop_fd, LOOP_CTL_GET_FREE);
+		next_loop = ioctl(next_loop_fd, LOOP_CTL_GET_FREE);
+		if (next_loop < 0) {
 			close(next_loop_fd);
-			if (next_loop < 0)
-				return NULL;
+			return NULL;
 		}
-
 		sprintf(dev, "/dev/loop%d", next_loop);
 
 		fd = open (dev, O_RDONLY);
@@ -199,6 +201,9 @@  char *find_unused_loop_device(void)
 		}
 		break;
 	}
+
+	close(next_loop_fd);
+
 	if (next_loop_dev)
 		return next_loop_dev;