nfsd: Fix handling of negative lengths in read_buf()

The length "nbytes" passed into read_buf should never be negative, but
we check only for too-large values of "nbytes", not for too-small
values.  Make nbytes unsigned, so it's clear that the former tests are
sufficient.  (Despite this read_buf() currently correctly returns an xdr
error in the case of a negative length, thanks to an unsigned
comparison with size_of() and bounds-checking in kmalloc().  This seems
very fragile, though.)

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 5733394..bf1e792 100644 (file)
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -148,12 +148,12 @@ xdr_error:                                        \
        }                                       \
 } while (0)
 
-static __be32 *read_buf(struct nfsd4_compoundargs *argp, int nbytes)
+static __be32 *read_buf(struct nfsd4_compoundargs *argp, u32 nbytes)
 {
        /* We want more bytes than seem to be available.
         * Maybe we need a new page, maybe we have just run out
         */
-       int avail = (char*)argp->end - (char*)argp->p;
+       unsigned int avail = (char *)argp->end - (char *)argp->p;
        __be32 *p;
        if (avail + argp->pagelen < nbytes)
                return NULL;
@@ -169,6 +169,11 @@ static __be32 *read_buf(struct nfsd4_compoundargs *argp, int nbytes)
                        return NULL;
                
        }
+       /*
+        * The following memcpy is safe because read_buf is always
+        * called with nbytes > avail, and the two cases above both
+        * guarantee p points to at least nbytes bytes.
+        */
        memcpy(p, argp->p, avail);
        /* step to next page */
        argp->p = page_address(argp->pagelist[0]);