From 676e4ebd5f2c3b4fd1d2bff79b68385c23c5c105 Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Tue, 30 Apr 2013 18:48:54 -0400 Subject: [PATCH] NFSD: SECINFO doesn't handle unsupported pseudoflavors correctly If nfsd4_do_encode_secinfo() can't find GSS info that matches an export security flavor, it assumes the flavor is not a GSS pseudoflavor, and simply puts it on the wire. However, if this XDR encoding logic is given a legitimate GSS pseudoflavor but the RPC layer says it does not support that pseudoflavor for some reason, then the server leaks GSS pseudoflavor numbers onto the wire. I confirmed this happens by blacklisting rpcsec_gss_krb5, then attempted a client transition from the pseudo-fs to a Kerberos-only share. The client received a flavor list containing the Kerberos pseudoflavor numbers, rather than GSS tuples. The encoder logic can check that each pseudoflavor in flavs[] is less than MAXFLAVOR before writing it into the buffer, to prevent this. But after "nflavs" is written into the XDR buffer, the encoder can't skip writing flavor information into the buffer when it discovers the RPC layer doesn't support that flavor. So count the number of valid flavors as they are written into the XDR buffer, then write that count into a placeholder in the XDR buffer when all recognized flavors have been encoded. Signed-off-by: Chuck Lever Signed-off-by: J. Bruce Fields --- fs/nfsd/nfs4xdr.c | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-) diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c index a885e97dc5f4..6cd86e0fe450 100644 --- a/fs/nfsd/nfs4xdr.c +++ b/fs/nfsd/nfs4xdr.c @@ -3085,10 +3085,11 @@ static __be32 nfsd4_do_encode_secinfo(struct nfsd4_compoundres *resp, __be32 nfserr, struct svc_export *exp) { - u32 i, nflavs; + u32 i, nflavs, supported; struct exp_flavor_info *flavs; struct exp_flavor_info def_flavs[2]; - __be32 *p; + __be32 *p, *flavorsp; + static bool report = true; if (nfserr) goto out; @@ -3112,13 +3113,17 @@ nfsd4_do_encode_secinfo(struct nfsd4_compoundres *resp, } } + supported = 0; RESERVE_SPACE(4); - WRITE32(nflavs); + flavorsp = p++; /* to be backfilled later */ ADJUST_ARGS(); + for (i = 0; i < nflavs; i++) { + rpc_authflavor_t pf = flavs[i].pseudoflavor; struct rpcsec_gss_info info; - if (rpcauth_get_gssinfo(flavs[i].pseudoflavor, &info) == 0) { + if (rpcauth_get_gssinfo(pf, &info) == 0) { + supported++; RESERVE_SPACE(4 + 4 + info.oid.len + 4 + 4); WRITE32(RPC_AUTH_GSS); WRITE32(info.oid.len); @@ -3126,13 +3131,22 @@ nfsd4_do_encode_secinfo(struct nfsd4_compoundres *resp, WRITE32(info.qop); WRITE32(info.service); ADJUST_ARGS(); - } else { + } else if (pf < RPC_AUTH_MAXFLAVOR) { + supported++; RESERVE_SPACE(4); - WRITE32(flavs[i].pseudoflavor); + WRITE32(pf); ADJUST_ARGS(); + } else { + if (report) + pr_warn("NFS: SECINFO: security flavor %u " + "is not supported\n", pf); } } + if (nflavs != supported) + report = false; + *flavorsp = htonl(supported); + out: if (exp) exp_put(exp);