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SubjectRe: [PATCH] nfs client, kernel 2.4.31: readlink result overflow
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Date
Valdis.Kletnieks@vt.edu writes:
> > To my reading, the 2.6.13 code does not copy the 4 bytes of length to
> > rcvbuf.
>
> Hmm... it still does this:
> kaddr[len+rcvbuf->page_base] = '\0';
> which still has a possible off-by-one? (Was that why you have -1 -4?)

The check is different. 2.6.13 is using ">=" instead of ">", so hence
I think that's fine.

> sizeof(actual_var) is even better, as that way it's clear what you're allowing
> space for.

diff -u linux-2.4.31.orig/fs/nfs/nfs2xdr.c linux-2.4.31/fs/nfs/nfs2xdr.c
--- linux-2.4.31.orig/fs/nfs/nfs2xdr.c 2002-11-28 18:53:15.000000000 -0500
+++ linux-2.4.31/fs/nfs/nfs2xdr.c 2005-09-12 16:12:30.000000000 -0400
@@ -571,8 +571,8 @@
strlen = (u32*)kmap(rcvbuf->pages[0]);
/* Convert length of symlink */
len = ntohl(*strlen);
- if (len > rcvbuf->page_len)
- len = rcvbuf->page_len;
+ if (len > rcvbuf->page_len - sizeof(*strlen) - 1)
+ len = rcvbuf->page_len - sizeof(*strlen) - 1;
*strlen = len;
/* NULL terminate the string we got */
string = (char *)(strlen + 1);
diff -u linux-2.4.31.orig/fs/nfs/nfs3xdr.c linux-2.4.31/fs/nfs/nfs3xdr.c
--- linux-2.4.31.orig/fs/nfs/nfs3xdr.c 2003-11-28 13:26:21.000000000 -0500
+++ linux-2.4.31/fs/nfs/nfs3xdr.c 2005-09-12 16:12:29.000000000 -0400
@@ -759,8 +759,8 @@
strlen = (u32*)kmap(rcvbuf->pages[0]);
/* Convert length of symlink */
len = ntohl(*strlen);
- if (len > rcvbuf->page_len)
- len = rcvbuf->page_len;
+ if (len > rcvbuf->page_len - sizeof(*strlen) - 1)
+ len = rcvbuf->page_len - sizeof(*strlen) - 1;
*strlen = len;
/* NULL terminate the string we got */
string = (char *)(strlen + 1);
-
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