SUNRPC: svcauth_gss: avoid NULL deref on zero length gss_token in gss_read_proxy_verf

A zero length gss_token results in pages == 0 and in_token->pages[0]
is NULL. The code unconditionally evaluates
page_address(in_token->pages[0]) for the initial memcpy, which can
dereference NULL even when the copy length is 0. Guard the first
memcpy so it only runs when length > 0.

Fixes: 5866efa8cbfb ("SUNRPC: Fix svcauth_gss_proxy_init()")
Cc: stable@vger.kernel.org
Signed-off-by: Joshua Rogers <linux@joshua.hu>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
index a8ec30759a184e22f8e588ab71b243db7026e1b7..e2f0df8cdaa6a0af07b47fd885073a0a78866da3 100644 (file)
--- a/net/sunrpc/auth_gss/svcauth_gss.c
+++ b/net/sunrpc/auth_gss/svcauth_gss.c
@@ -1083,7 +1083,8 @@ static int gss_read_proxy_verf(struct svc_rqst *rqstp,
        }
 
        length = min_t(unsigned int, inlen, (char *)xdr->end - (char *)xdr->p);
-       memcpy(page_address(in_token->pages[0]), xdr->p, length);
+       if (length)
+               memcpy(page_address(in_token->pages[0]), xdr->p, length);
        inlen -= length;
 
        to_offs = length;