nfsd4: bug in read_buf

commit 2bc3c1179c781b359d4f2f3439cb3df72afc17fc upstream.

When read_buf is called to move over to the next page in the pagelist
of an NFSv4 request, it sets argp->end to essentially a random
number, certainly not an address within the page which argp->p now
points to.  So subsequent calls to READ_BUF will think there is much
more than a page of spare space (the cast to u32 ensures an unsigned
comparison) so we can expect to fall off the end of the second
page.

We never encountered thsi in testing because typically the only
operations which use more than two pages are write-like operations,
which have their own decoding logic.  Something like a getattr after a
write may cross a page boundary, but it would be very unusual for it to
cross another boundary after that.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index abffc9057b0f5078412ca8ddc67be889bf939c67..6203c81d30805fbe9910f61be03e3014416d73c3 100644 (file)
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -179,10 +179,10 @@ static __be32 *read_buf(struct nfsd4_compoundargs *argp, u32 nbytes)
        argp->p = page_address(argp->pagelist[0]);
        argp->pagelist++;
        if (argp->pagelen < PAGE_SIZE) {
-               argp->end = p + (argp->pagelen>>2);
+               argp->end = argp->p + (argp->pagelen>>2);
                argp->pagelen = 0;
        } else {
-               argp->end = p + (PAGE_SIZE>>2);
+               argp->end = argp->p + (PAGE_SIZE>>2);
                argp->pagelen -= PAGE_SIZE;
        }
        memcpy(((char*)p)+avail, argp->p, (nbytes - avail));
@@ -1115,10 +1115,10 @@ nfsd4_decode_compound(struct nfsd4_compoundargs *argp)
                        argp->p = page_address(argp->pagelist[0]);
                        argp->pagelist++;
                        if (argp->pagelen < PAGE_SIZE) {
-                               argp->end = p + (argp->pagelen>>2);
+                               argp->end = argp->p + (argp->pagelen>>2);
                                argp->pagelen = 0;
                        } else {
-                               argp->end = p + (PAGE_SIZE>>2);
+                               argp->end = argp->p + (PAGE_SIZE>>2);
                                argp->pagelen -= PAGE_SIZE;
                        }
                }