slash appended to filesystem when mtab symlinked to proc

Hi

A Debian user reported a bug that a slash gets appended to the filesystem when he mounts a share. This only happens when mtab is symlinked to proc which I can reproduce:

$ grep cifs /etc/fstab
//<host>/<path>	/mnt	cifs	user,user=<username>	0	0

$ mount /mnt

$ grep cifs /etc/mtab
//<host>/<path>/ /mnt cifs
rw,nosuid,nodev,relatime,unc=\\<host>\<path>,username=<username>,uid=1000,forceuid,gid=1000,forcegid,addr=<ip>,file_mode=0755,dir_mode=0755,serverino,rsize=16384,wsize=57344
0 0

$ umount /mnt
umount: /mnt mount disagrees with the fstab

There does not seem to be any other filesystems that append a slash to the filesystem in proc. Does cifsfs do that intentionally (in which case the client should cope with it: by means of umount.cifs?) or should it get fixed in the kernel (maybe the client should still cope with it)?

Can you give me a hand in identifying the code that would need to be updated to fix this so I can prepare a patch?

Cheers

Luk

When dev_name is constructed by combining slashes with the different parsed_mount_info fields, there can be an unnecessary appended slash compared to the original device string. So only convert backslashes to slashes to get the device name from the original device string.

Signed-off-by Luk Claes <[email protected]>

---
 mount.cifs.c |   15 +++++----------
 1 files changed, 5 insertions(+), 10 deletions(-)

mount.cifs.c +1 -7

index 8e1e32b..2cec7e4 100644
@@ -1824,10 +1824,7 @@ int main(int argc, char **argv)
 	}
 
 	/* lengths of different strings + slashes + trailing \0 */
-	dev_len = strnlen(parsed_info->host, sizeof(parsed_info->host)) +
-	    strnlen(parsed_info->share, sizeof(parsed_info->share)) +
-	    strnlen(parsed_info->prefix, sizeof(parsed_info->prefix)) +
-	    2 + 1 + 1 + 1;
+	dev_len = strlen(orig_dev) + 1;
 	dev_name = calloc(dev_len, 1);
 	if (!dev_name) {
 		rc = EX_SYSERR;

@@ -1835,12 +1832,10 @@ int main(int argc, char **argv)
 	}
 
 	/* rebuild device name with forward slashes */
-	strlcpy(dev_name, "//", dev_len);
-	strlcat(dev_name, parsed_info->host, dev_len);
-	strlcat(dev_name, "/", dev_len);

Don't construct a device name, but use the original device string to mount so the device name in /proc/mounts matches the one in /etc/fstab.

Signed-off-by Luk Claes <[email protected]>

---
 mount.cifs.c |   27 +++------------------------
 1 files changed, 3 insertions(+), 24 deletions(-)

mount.cifs.c +3 -23

index 8e1e32b..29b0d4c 100644
@@ -1673,12 +1673,11 @@ int main(int argc, char **argv)
 	char *orgoptions = NULL;
 	char *mountpoint = NULL;
 	char *options = NULL;
-	char *dev_name = NULL, *orig_dev = NULL;
+	char *orig_dev = NULL;
 	char *currentaddress, *nextaddress;
 	int rc = 0;
 	int already_uppercased = 0;
 	size_t options_size = MAX_OPTIONS_LEN;
-	size_t dev_len;
 	struct parsed_mount_info *parsed_info = NULL;
 	pid_t pid;
 	const char *fstype;

@@ -1823,25 +1822,6 @@ int main(int argc, char **argv)
 		goto mount_exit;
 	}
 
-	/* lengths of different strings + slashes + trailing \0 */
-	dev_len = strnlen(parsed_info->host, sizeof(parsed_info->host)) +
-	    strnlen(parsed_info->share, sizeof(parsed_info->share)) +
-	    strnlen(parsed_info->prefix, sizeof(parsed_info->prefix)) +
-	    2 + 1 + 1 + 1;
-	dev_name = calloc(dev_len, 1);
-	if (!dev_name) {
-		rc = EX_SYSERR;
-		goto mount_exit;
-	}
-
-	/* rebuild device name with forward slashes */
-	strlcpy(dev_name, "//", dev_len);
-	strlcat(dev_name, parsed_info->host, dev_len);
-	strlcat(dev_name, "/", dev_len);
-	strlcat(dev_name, parsed_info->share, dev_len);
-	strlcat(dev_name, "/", dev_len);
-	strlcat(dev_name, parsed_info->prefix, dev_len);
-
 	currentaddress = parsed_info->addrlist;
 	nextaddress = strchr(currentaddress, ',');
 	if (nextaddress)

@@ -1889,7 +1869,7 @@ mount_retry:
 	if (parsed_info->verboseflag)
 		fprintf(stderr, "\n");
 
-	rc = check_mtab(thisprogram, dev_name, mountpoint);
+	rc = check_mtab(thisprogram, orig_dev, mountpoint);
 	if (rc)
 		goto mount_exit;
 

@@ -1900,7 +1880,7 @@ mount_retry:
 
 	if (!parsed_info->fakemnt) {
 		toggle_dac_capability(0, 1);
-		rc = mount(dev_name, ".", fstype, parsed_info->flags, options);
+		rc = mount(orig_dev, ".", fstype, parsed_info->flags, options);
 		toggle_dac_capability(0, 0);
 		if (rc == 0)
 			goto do_mtab;