[PATCH v2] cifs: fix regression when mounting shares with prefix paths

Paulo Alcantara
2021-05-03T14:55:54Z

The commit 315db9a05b7a ("cifs: fix leak in cifs_smb3_do_mount() ctx")
revealed an existing bug when mounting shares that contain a prefix
path or DFS links.

cifs_setup_volume_info() requires the @devname to contain the full
path (UNC + prefix) to update the fs context with the new UNC and
prepath values, however we were passing only the UNC
path (old_ctx->UNC) in @device thus discarding any prefix paths.

Instead of concatenating both old_ctx->{UNC,prepath} and pass it in
@devname, just keep the dup'ed values of UNC and prepath in
cifs_sb->ctx after calling smb3_fs_context_dup(), and fix
smb3_parse_devname() to correctly parse and not leak the new UNC and
prefix paths.

Cc: <stable@vger.kernel.org> # v5.11+
Fixes: 315db9a05b7a ("cifs: fix leak in cifs_smb3_do_mount() ctx")
Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
---
fs/cifs/cifsfs.c | 8 +-------
fs/cifs/connect.c | 24 ++++++++++++++++++------
fs/cifs/fs_context.c | 4 ++++
3 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index 8a6894577697..d7ea9c5fe0f8 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -863,13 +863,7 @@ cifs_smb3_do_mount(struct file_system_type *fs_type,
goto out;
}

- /* cifs_setup_volume_info->smb3_parse_devname() redups UNC & prepath */
- kfree(cifs_sb->ctx->UNC);
- cifs_sb->ctx->UNC = NULL;
- kfree(cifs_sb->ctx->prepath);
- cifs_sb->ctx->prepath = NULL;
-
- rc = cifs_setup_volume_info(cifs_sb->ctx, NULL, old_ctx->UNC);
+ rc = cifs_setup_volume_info(cifs_sb->ctx, NULL, NULL);
if (rc) {
root = ERR_PTR(rc);
goto out;
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index becd5f807787..4ce6fc24cae1 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -3159,17 +3159,29 @@ static int do_dfs_failover(const char *path, const char *full_path, struct cifs_
int
cifs_setup_volume_info(struct smb3_fs_context *ctx, const char *mntopts, const char *devname)
{
- int rc = 0;
+ int rc;

- smb3_parse_devname(devname, ctx);
+ if (devname) {
+ cifs_dbg(FYI, "%s: devname=%s\n", __func__, devname);
+ rc = smb3_parse_devname(devname, ctx);
+ if (rc) {
+ cifs_dbg(VFS, "%s: failed to parse %s: %d\n", __func__, devname, rc);
+ return rc;
+ }
+ }

if (mntopts) {
char *ip;

- cifs_dbg(FYI, "%s: mntopts=%s\n", __func__, mntopts);
rc = smb3_parse_opt(mntopts, "ip", &ip);
- if (!rc && !cifs_convert_address((struct sockaddr *)&ctx->dstaddr, ip,
- strlen(ip))) {
+ if (rc) {
+ cifs_dbg(VFS, "%s: failed to parse ip options: %d\n", __func__, rc);
+ return rc;
+ }
+
+ rc = cifs_convert_address((struct sockaddr *)&ctx->dstaddr, ip, strlen(ip));
+ kfree(ip);
+ if (!rc) {
cifs_dbg(VFS, "%s: failed to convert ip address\n", __func__);
return -EINVAL;
}
@@ -3189,7 +3201,7 @@ cifs_setup_volume_info(struct smb3_fs_context *ctx, const char *mntopts, const c
return -EINVAL;
}

- return rc;
+ return 0;
}

static int
diff --git a/fs/cifs/fs_context.c b/fs/cifs/fs_context.c
index 1d6e0e15b034..3bcf881c3ae9 100644
--- a/fs/cifs/fs_context.c
+++ b/fs/cifs/fs_context.c
@@ -476,6 +476,7 @@ smb3_parse_devname(const char *devname, struct smb3_fs_context *ctx)

/* move "pos" up to delimiter or NULL */
pos += len;
+ kfree(ctx->UNC);
ctx->UNC = kstrndup(devname, pos - devname, GFP_KERNEL);
if (!ctx->UNC)
return -ENOMEM;
@@ -486,6 +487,9 @@ smb3_parse_devname(const char *devname, struct smb3_fs_context *ctx)
if (*pos == '/' || *pos == '\\')
pos++;

+ kfree(ctx->prepath);
+ ctx->prepath = NULL;
+
/* If pos is NULL then no prepath */
if (!*pos)
return 0;
--
2.31.1