nfsd: check for oversized NFSv2/v3 arguments (CVE-2017-7645)
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@ -373,6 +373,7 @@ linux (4.9.25-1) UNRELEASED; urgency=medium
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* ping: implement proper locking (CVE-2017-2671)
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* macsec: avoid heap overflow in skb_to_sgvec (CVE-2017-7477)
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* macsec: dynamically allocate space for sglist
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* nfsd: check for oversized NFSv2/v3 arguments (CVE-2017-7645)
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[ Aurelien Jarno ]
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* [mips*/octeon] Drop obsolete patch adding support for the UBNT E200
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104
debian/patches/bugfix/all/nfsd-check-for-oversized-NFSv2-v3-arguments.patch
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104
debian/patches/bugfix/all/nfsd-check-for-oversized-NFSv2-v3-arguments.patch
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@ -0,0 +1,104 @@
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From: "J. Bruce Fields" <bfields@redhat.com>
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Date: Fri, 21 Apr 2017 16:10:18 -0400
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Subject: nfsd: check for oversized NFSv2/v3 arguments
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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Origin: https://git.kernel.org/linus/e6838a29ecb484c97e4efef9429643b9851fba6e
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Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2017-7645
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A client can append random data to the end of an NFSv2 or NFSv3 RPC call
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without our complaining; we'll just stop parsing at the end of the
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expected data and ignore the rest.
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Encoded arguments and replies are stored together in an array of pages,
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and if a call is too large it could leave inadequate space for the
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reply. This is normally OK because NFS RPC's typically have either
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short arguments and long replies (like READ) or long arguments and short
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replies (like WRITE). But a client that sends an incorrectly long reply
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can violate those assumptions. This was observed to cause crashes.
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Also, several operations increment rq_next_page in the decode routine
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before checking the argument size, which can leave rq_next_page pointing
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well past the end of the page array, causing trouble later in
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svc_free_pages.
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So, following a suggestion from Neil Brown, add a central check to
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enforce our expectation that no NFSv2/v3 call has both a large call and
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a large reply.
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As followup we may also want to rewrite the encoding routines to check
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more carefully that they aren't running off the end of the page array.
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We may also consider rejecting calls that have any extra garbage
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appended. That would be safer, and within our rights by spec, but given
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the age of our server and the NFS protocol, and the fact that we've
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never enforced this before, we may need to balance that against the
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possibility of breaking some oddball client.
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Reported-by: Tuomas Haanpää <thaan@synopsys.com>
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Reported-by: Ari Kauppi <ari@synopsys.com>
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Cc: stable@vger.kernel.org
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Reviewed-by: NeilBrown <neilb@suse.com>
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Signed-off-by: J. Bruce Fields <bfields@redhat.com>
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---
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fs/nfsd/nfssvc.c | 36 ++++++++++++++++++++++++++++++++++++
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1 file changed, 36 insertions(+)
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diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
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index 31e1f95..59979f0 100644
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--- a/fs/nfsd/nfssvc.c
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+++ b/fs/nfsd/nfssvc.c
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@@ -747,6 +747,37 @@ static __be32 map_new_errors(u32 vers, __be32 nfserr)
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return nfserr;
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}
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+/*
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+ * A write procedure can have a large argument, and a read procedure can
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+ * have a large reply, but no NFSv2 or NFSv3 procedure has argument and
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+ * reply that can both be larger than a page. The xdr code has taken
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+ * advantage of this assumption to be a sloppy about bounds checking in
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+ * some cases. Pending a rewrite of the NFSv2/v3 xdr code to fix that
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+ * problem, we enforce these assumptions here:
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+ */
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+static bool nfs_request_too_big(struct svc_rqst *rqstp,
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+ struct svc_procedure *proc)
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+{
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+ /*
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+ * The ACL code has more careful bounds-checking and is not
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+ * susceptible to this problem:
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+ */
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+ if (rqstp->rq_prog != NFS_PROGRAM)
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+ return false;
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+ /*
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+ * Ditto NFSv4 (which can in theory have argument and reply both
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+ * more than a page):
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+ */
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+ if (rqstp->rq_vers >= 4)
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+ return false;
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+ /* The reply will be small, we're OK: */
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+ if (proc->pc_xdrressize > 0 &&
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+ proc->pc_xdrressize < XDR_QUADLEN(PAGE_SIZE))
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+ return false;
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+
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+ return rqstp->rq_arg.len > PAGE_SIZE;
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+}
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+
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int
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nfsd_dispatch(struct svc_rqst *rqstp, __be32 *statp)
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{
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@@ -759,6 +790,11 @@ nfsd_dispatch(struct svc_rqst *rqstp, __be32 *statp)
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rqstp->rq_vers, rqstp->rq_proc);
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proc = rqstp->rq_procinfo;
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+ if (nfs_request_too_big(rqstp, proc)) {
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+ dprintk("nfsd: NFSv%d argument too large\n", rqstp->rq_vers);
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+ *statp = rpc_garbage_args;
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+ return 1;
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+ }
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/*
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* Give the xdr decoder a chance to change this if it wants
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* (necessary in the NFSv4.0 compound case)
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--
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2.1.4
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@ -110,6 +110,7 @@ bugfix/all/net-packet-fix-overflow-in-check-for-tp_reserve.patch
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bugfix/all/ping-implement-proper-locking.patch
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bugfix/all/macsec-avoid-heap-overflow-in-skb_to_sgvec.patch
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bugfix/all/macsec-dynamically-allocate-space-for-sglist.patch
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bugfix/all/nfsd-check-for-oversized-NFSv2-v3-arguments.patch
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# Fix exported symbol versions
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bugfix/ia64/revert-ia64-move-exports-to-definitions.patch
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