[PATCH] cifs: fix out-of-bound memory access when calling smb3_notify() at mount point

[PATCH] cifs: fix out-of-bound memory access when calling smb3_notify() at mount point

[Eugene Korenevsky]

If smb3_notify() is called at mount point of CIFS, build_path_from_dentry()
returns the pointer to kmalloc-ed memory with terminating zero (this is
empty FileName to be passed to SMB2 CREATE request). This pointer is assigned
to the `path` variable.
Then `path + 1` (to skip first backslash symbol) is passed to
cifs_convert_path_to_utf16(). This is incorrect for empty path and causes
out-of-bound memory access.

Get rid of this "increase by one". cifs_convert_path_to_utf16() already
contains the check for leading backslash in the path.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=212693
Signed-off-by: Eugene Korenevsky <ekorenevsky@astralinux.ru>
---
 fs/cifs/smb2ops.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index caa5432a5ed1..b13a8e3e1e24 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -2264,7 +2264,7 @@ smb3_notify(const unsigned int xid, struct file *pfile,
 		goto notify_exit;
 	}
 
-	utf16_path = cifs_convert_path_to_utf16(path + 1, cifs_sb);
+	utf16_path = cifs_convert_path_to_utf16(path, cifs_sb);
 	if (utf16_path == NULL) {
 		rc = -ENOMEM;
 		goto notify_exit;
-- 
2.20.1

Re: [PATCH] cifs: fix out-of-bound memory access when calling smb3_notify() at mount point

[Steve French]

Added:
   CC: <stable@vger.kernel.org> # v5.6+
and merged into cifs-2.6.git for-next

On Fri, Apr 16, 2021 at 2:42 AM Eugene Korenevsky
<ekorenevsky@astralinux.ru> wrote:
>
> If smb3_notify() is called at mount point of CIFS, build_path_from_dentry()
> returns the pointer to kmalloc-ed memory with terminating zero (this is
> empty FileName to be passed to SMB2 CREATE request). This pointer is assigned
> to the `path` variable.
> Then `path + 1` (to skip first backslash symbol) is passed to
> cifs_convert_path_to_utf16(). This is incorrect for empty path and causes
> out-of-bound memory access.
>
> Get rid of this "increase by one". cifs_convert_path_to_utf16() already
> contains the check for leading backslash in the path.
>
> BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=212693
> Signed-off-by: Eugene Korenevsky <ekorenevsky@astralinux.ru>
> ---
>  fs/cifs/smb2ops.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> index caa5432a5ed1..b13a8e3e1e24 100644
> --- a/fs/cifs/smb2ops.c
> +++ b/fs/cifs/smb2ops.c
> @@ -2264,7 +2264,7 @@ smb3_notify(const unsigned int xid, struct file *pfile,
>                 goto notify_exit;
>         }
>
> -       utf16_path = cifs_convert_path_to_utf16(path + 1, cifs_sb);
> +       utf16_path = cifs_convert_path_to_utf16(path, cifs_sb);
>         if (utf16_path == NULL) {
>                 rc = -ENOMEM;
>                 goto notify_exit;
> --
> 2.20.1
>


-- 
Thanks,

Steve