cifs: potential buffer overflow in handling symlinks

Smatch printed a warning:
	arch/x86/crypto/poly1305_glue.c:198 poly1305_update_arch() error:
	__memcpy() 'dctx->buf' too small (16 vs u32max)

It's caused because Smatch marks 'link_len' as untrusted since it comes
from sscanf(). Add a check to ensure that 'link_len' is not larger than
the size of the 'link_str' buffer.

Fixes: c69c1b6eaea1 ("cifs: implement CIFSParseMFSymlink()")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/cifs/link.c b/fs/cifs/link.c
index 852e54ee82c28279c00e6013b19916f3815a8b70..bbdf3281559c8f53c0e2c9d281f8fd5b4921e11b 100644 (file)
--- a/fs/cifs/link.c
+++ b/fs/cifs/link.c
@@ -85,6 +85,9 @@ parse_mf_symlink(const u8 *buf, unsigned int buf_len, unsigned int *_link_len,
        if (rc != 1)
                return -EINVAL;
 
+       if (link_len > CIFS_MF_SYMLINK_LINK_MAXLEN)
+               return -EINVAL;
+
        rc = symlink_hash(link_len, link_str, md5_hash);
        if (rc) {
                cifs_dbg(FYI, "%s: MD5 hash failure: %d\n", __func__, rc);