[PATCH 5.15 140/177] cifs: sanitize multiple delimiters in prepath

Greg Kroah-Hartman
2021-12-20T15:20:17Z

From: Thiago Rafael Becker <trbecker@gmail.com>

commit a31080899d5fdafcccf7f39dd214a814a2c82626 upstream.

mount.cifs can pass a device with multiple delimiters in it. This will
cause rename(2) to fail with ENOENT.

V2:
- Make sanitize_path more readable.
- Fix multiple delimiters between UNC and prepath.
- Avoid a memory leak if a bad user starts putting a lot of delimiters
in the path on purpose.

BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=2031200
Fixes: 24e0a1eff9e2 ("cifs: switch to new mount api")
Cc: stable@vger.kernel.org # 5.11+
Acked-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Thiago Rafael Becker <trbecker@gmail.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/cifs/fs_context.c | 38 +++++++++++++++++++++++++++++++++++++-
1 file changed, 37 insertions(+), 1 deletion(-)

--- a/fs/cifs/fs_context.c
+++ b/fs/cifs/fs_context.c
@@ -432,6 +432,42 @@ out:
}

/*
+ * Remove duplicate path delimiters. Windows is supposed to do that
+ * but there are some bugs that prevent rename from working if there are
+ * multiple delimiters.
+ *
+ * Returns a sanitized duplicate of @path. The caller is responsible for
+ * cleaning up the original.
+ */
+#define IS_DELIM(c) ((c) == '/' || (c) == '\\')
+static char *sanitize_path(char *path)
+{
+ char *cursor1 = path, *cursor2 = path;
+
+ /* skip all prepended delimiters */
+ while (IS_DELIM(*cursor1))
+ cursor1++;
+
+ /* copy the first letter */
+ *cursor2 = *cursor1;
+
+ /* copy the remainder... */
+ while (*(cursor1++)) {
+ /* ... skipping all duplicated delimiters */
+ if (IS_DELIM(*cursor1) && IS_DELIM(*cursor2))
+ continue;
+ *(++cursor2) = *cursor1;
+ }
+
+ /* if the last character is a delimiter, skip it */
+ if (IS_DELIM(*(cursor2 - 1)))
+ cursor2--;
+
+ *(cursor2) = '\0';
+ return kstrdup(path, GFP_KERNEL);
+}
+
+/*
* Parse a devname into substrings and populate the ctx->UNC and ctx->prepath
* fields with the result. Returns 0 on success and an error otherwise
* (e.g. ENOMEM or EINVAL)
@@ -490,7 +526,7 @@ smb3_parse_devname(const char *devname,
if (!*pos)
return 0;

- ctx->prepath = kstrdup(pos, GFP_KERNEL);
+ ctx->prepath = sanitize_path(pos);
if (!ctx->prepath)
return -ENOMEM;