Messages in this thread | | | Date | Tue, 13 Sep 2005 15:39:48 -0300 | From | Marcelo Tosatti <> | Subject | Re: [PATCH] nfs client, kernel 2.4.31: readlink result overflow |
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Hi Assar,
On Mon, Sep 12, 2005 at 04:41:19PM -0400, Assar wrote: > 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;
So the problem is that the "len" variable encapsulated in (u32 *)rcvbuf->pages[0] does not account for its own length (4 bytes)?
If thats the reason, you don't need the "-1" there?
Someone with better understanding to ACK this would be nice. Trond?
> *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); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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