cifs: potential memory leaks when parsing mnt opts

For example, when mount opt is redundently specified
(e.g., "user=A,user=B,user=C"), kernel kept allocating new key/val
with kstrdup() and overwrite previous ptr (to be freed).

Althouhg mount.cifs in userspace performs a bit of sanitization
(e.g., forcing one user option), current implementation is not
robust. Other options such as iocharset and domainanme are similarly
vulnerable.

Signed-off-by: Taesoo Kim <tsgatesv@gmail.com>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index d3aa999ab785..4cb8450e081b 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -1599,6 +1599,8 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
                                 pr_warn("CIFS: username too long\n");
                                 goto cifs_parse_mount_err;
                         }
+
+                        kfree(vol->username);
                         vol->username = kstrdup(string, GFP_KERNEL);
                         if (!vol->username)
                                 goto cifs_parse_mount_err;
@@ -1700,6 +1702,7 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
                                 goto cifs_parse_mount_err;
                         }
 
+                        kfree(vol->domainname);
                         vol->domainname = kstrdup(string, GFP_KERNEL);
                         if (!vol->domainname) {
                                 pr_warn("CIFS: no memory for domainname\n");
@@ -1731,6 +1734,7 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
                         }
 
                          if (strncasecmp(string, "default", 7) != 0) {
+                                kfree(vol->iocharset);
                                 vol->iocharset = kstrdup(string,
                                                          GFP_KERNEL);
                                 if (!vol->iocharset) {