[PATCH 3.18 15/22] nfsd: Limit end of page list when decoding NFSv4 WRITE

Greg Kroah-Hartman
2017-08-28T08:16:28Z

From: Chuck Lever <chuck.lever@oracle.com>

commit fc788f64f1f3eb31e87d4f53bcf1ab76590d5838 upstream.

When processing an NFSv4 WRITE operation, argp->end should never
point past the end of the data in the final page of the page list.
Otherwise, nfsd4_decode_compound can walk into uninitialized memory.

More critical, nfsd4_decode_write is failing to increment argp->pagelen
when it increments argp->pagelist. This can cause later xdr decoders
to assume more data is available than really is, which can cause server
crashes on malformed requests.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/nfsd/nfs4xdr.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -127,7 +127,7 @@ static void next_decode_page(struct nfsd
argp->p = page_address(argp->pagelist[0]);
argp->pagelist++;
if (argp->pagelen < PAGE_SIZE) {
- argp->end = argp->p + (argp->pagelen>>2);
+ argp->end = argp->p + XDR_QUADLEN(argp->pagelen);
argp->pagelen = 0;
} else {
argp->end = argp->p + (PAGE_SIZE>>2);
@@ -1235,9 +1235,7 @@ nfsd4_decode_write(struct nfsd4_compound
argp->pagelen -= pages * PAGE_SIZE;
len -= pages * PAGE_SIZE;

- argp->p = (__be32 *)page_address(argp->pagelist[0]);
- argp->pagelist++;
- argp->end = argp->p + XDR_QUADLEN(PAGE_SIZE);
+ next_decode_page(argp);
}
argp->p += XDR_QUADLEN(len);