From e6838a29ecb484c97e4efef9429643b9851fba6e Mon Sep 17 00:00:00 2001 From: "J. Bruce Fields" Date: Fri, 21 Apr 2017 16:10:18 -0400 Subject: [PATCH 1/3] nfsd: check for oversized NFSv2/v3 arguments MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit A client can append random data to the end of an NFSv2 or NFSv3 RPC call without our complaining; we'll just stop parsing at the end of the expected data and ignore the rest. Encoded arguments and replies are stored together in an array of pages, and if a call is too large it could leave inadequate space for the reply. This is normally OK because NFS RPC's typically have either short arguments and long replies (like READ) or long arguments and short replies (like WRITE). But a client that sends an incorrectly long reply can violate those assumptions. This was observed to cause crashes. Also, several operations increment rq_next_page in the decode routine before checking the argument size, which can leave rq_next_page pointing well past the end of the page array, causing trouble later in svc_free_pages. So, following a suggestion from Neil Brown, add a central check to enforce our expectation that no NFSv2/v3 call has both a large call and a large reply. As followup we may also want to rewrite the encoding routines to check more carefully that they aren't running off the end of the page array. We may also consider rejecting calls that have any extra garbage appended. That would be safer, and within our rights by spec, but given the age of our server and the NFS protocol, and the fact that we've never enforced this before, we may need to balance that against the possibility of breaking some oddball client. Reported-by: Tuomas Haanpää Reported-by: Ari Kauppi Cc: stable@vger.kernel.org Reviewed-by: NeilBrown Signed-off-by: J. Bruce Fields --- fs/nfsd/nfssvc.c | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c index 31e1f9593457..59979f0bbd4b 100644 --- a/fs/nfsd/nfssvc.c +++ b/fs/nfsd/nfssvc.c @@ -747,6 +747,37 @@ static __be32 map_new_errors(u32 vers, __be32 nfserr) return nfserr; } +/* + * A write procedure can have a large argument, and a read procedure can + * have a large reply, but no NFSv2 or NFSv3 procedure has argument and + * reply that can both be larger than a page. The xdr code has taken + * advantage of this assumption to be a sloppy about bounds checking in + * some cases. Pending a rewrite of the NFSv2/v3 xdr code to fix that + * problem, we enforce these assumptions here: + */ +static bool nfs_request_too_big(struct svc_rqst *rqstp, + struct svc_procedure *proc) +{ + /* + * The ACL code has more careful bounds-checking and is not + * susceptible to this problem: + */ + if (rqstp->rq_prog != NFS_PROGRAM) + return false; + /* + * Ditto NFSv4 (which can in theory have argument and reply both + * more than a page): + */ + if (rqstp->rq_vers >= 4) + return false; + /* The reply will be small, we're OK: */ + if (proc->pc_xdrressize > 0 && + proc->pc_xdrressize < XDR_QUADLEN(PAGE_SIZE)) + return false; + + return rqstp->rq_arg.len > PAGE_SIZE; +} + int nfsd_dispatch(struct svc_rqst *rqstp, __be32 *statp) { @@ -759,6 +790,11 @@ nfsd_dispatch(struct svc_rqst *rqstp, __be32 *statp) rqstp->rq_vers, rqstp->rq_proc); proc = rqstp->rq_procinfo; + if (nfs_request_too_big(rqstp, proc)) { + dprintk("nfsd: NFSv%d argument too large\n", rqstp->rq_vers); + *statp = rpc_garbage_args; + return 1; + } /* * Give the xdr decoder a chance to change this if it wants * (necessary in the NFSv4.0 compound case) From db44bac41bbfc0c0d9dd943092d8bded3c9db19b Mon Sep 17 00:00:00 2001 From: "J. Bruce Fields" Date: Tue, 25 Apr 2017 16:21:34 -0400 Subject: [PATCH 2/3] nfsd4: minor NFSv2/v3 write decoding cleanup Use a couple shortcuts that will simplify a following bugfix. Cc: stable@vger.kernel.org Signed-off-by: J. Bruce Fields --- fs/nfsd/nfs3xdr.c | 9 +++++---- fs/nfsd/nfsxdr.c | 8 ++++---- 2 files changed, 9 insertions(+), 8 deletions(-) diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c index dba2ff8eaa68..d18cfddbe115 100644 --- a/fs/nfsd/nfs3xdr.c +++ b/fs/nfsd/nfs3xdr.c @@ -358,6 +358,8 @@ nfs3svc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p, { unsigned int len, v, hdr, dlen; u32 max_blocksize = svc_max_payload(rqstp); + struct kvec *head = rqstp->rq_arg.head; + struct kvec *tail = rqstp->rq_arg.tail; p = decode_fh(p, &args->fh); if (!p) @@ -377,9 +379,8 @@ nfs3svc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p, * Check to make sure that we got the right number of * bytes. */ - hdr = (void*)p - rqstp->rq_arg.head[0].iov_base; - dlen = rqstp->rq_arg.head[0].iov_len + rqstp->rq_arg.page_len - + rqstp->rq_arg.tail[0].iov_len - hdr; + hdr = (void*)p - head->iov_base; + dlen = head->iov_len + rqstp->rq_arg.page_len + tail->iov_len - hdr; /* * Round the length of the data which was specified up to * the next multiple of XDR units and then compare that @@ -396,7 +397,7 @@ nfs3svc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p, len = args->len = max_blocksize; } rqstp->rq_vec[0].iov_base = (void*)p; - rqstp->rq_vec[0].iov_len = rqstp->rq_arg.head[0].iov_len - hdr; + rqstp->rq_vec[0].iov_len = head->iov_len - hdr; v = 0; while (len > rqstp->rq_vec[v].iov_len) { len -= rqstp->rq_vec[v].iov_len; diff --git a/fs/nfsd/nfsxdr.c b/fs/nfsd/nfsxdr.c index 41b468a6a90f..59bd88a23a3d 100644 --- a/fs/nfsd/nfsxdr.c +++ b/fs/nfsd/nfsxdr.c @@ -280,6 +280,7 @@ nfssvc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p, struct nfsd_writeargs *args) { unsigned int len, hdr, dlen; + struct kvec *head = rqstp->rq_arg.head; int v; p = decode_fh(p, &args->fh); @@ -300,9 +301,8 @@ nfssvc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p, * Check to make sure that we got the right number of * bytes. */ - hdr = (void*)p - rqstp->rq_arg.head[0].iov_base; - dlen = rqstp->rq_arg.head[0].iov_len + rqstp->rq_arg.page_len - - hdr; + hdr = (void*)p - head->iov_base; + dlen = head->iov_len + rqstp->rq_arg.page_len - hdr; /* * Round the length of the data which was specified up to @@ -316,7 +316,7 @@ nfssvc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p, return 0; rqstp->rq_vec[0].iov_base = (void*)p; - rqstp->rq_vec[0].iov_len = rqstp->rq_arg.head[0].iov_len - hdr; + rqstp->rq_vec[0].iov_len = head->iov_len - hdr; v = 0; while (len > rqstp->rq_vec[v].iov_len) { len -= rqstp->rq_vec[v].iov_len; From 13bf9fbff0e5e099e2b6f003a0ab8ae145436309 Mon Sep 17 00:00:00 2001 From: "J. Bruce Fields" Date: Fri, 21 Apr 2017 15:26:30 -0400 Subject: [PATCH 3/3] nfsd: stricter decoding of write-like NFSv2/v3 ops MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The NFSv2/v3 code does not systematically check whether we decode past the end of the buffer. This generally appears to be harmless, but there are a few places where we do arithmetic on the pointers involved and don't account for the possibility that a length could be negative. Add checks to catch these. Reported-by: Tuomas Haanpää Reported-by: Ari Kauppi Reviewed-by: NeilBrown Cc: stable@vger.kernel.org Signed-off-by: J. Bruce Fields --- fs/nfsd/nfs3xdr.c | 4 ++++ fs/nfsd/nfsxdr.c | 2 ++ 2 files changed, 6 insertions(+) diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c index d18cfddbe115..452334694a5d 100644 --- a/fs/nfsd/nfs3xdr.c +++ b/fs/nfsd/nfs3xdr.c @@ -369,6 +369,8 @@ nfs3svc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p, args->count = ntohl(*p++); args->stable = ntohl(*p++); len = args->len = ntohl(*p++); + if ((void *)p > head->iov_base + head->iov_len) + return 0; /* * The count must equal the amount of data passed. */ @@ -472,6 +474,8 @@ nfs3svc_decode_symlinkargs(struct svc_rqst *rqstp, __be32 *p, /* first copy and check from the first page */ old = (char*)p; vec = &rqstp->rq_arg.head[0]; + if ((void *)old > vec->iov_base + vec->iov_len) + return 0; avail = vec->iov_len - (old - (char*)vec->iov_base); while (len && avail && *old) { *new++ = *old++; diff --git a/fs/nfsd/nfsxdr.c b/fs/nfsd/nfsxdr.c index 59bd88a23a3d..de07ff625777 100644 --- a/fs/nfsd/nfsxdr.c +++ b/fs/nfsd/nfsxdr.c @@ -302,6 +302,8 @@ nfssvc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p, * bytes. */ hdr = (void*)p - head->iov_base; + if (hdr > head->iov_len) + return 0; dlen = head->iov_len + rqstp->rq_arg.page_len - hdr; /*