From 4bc1108e876153a2dd6d874052b99182c3603135 Mon Sep 17 00:00:00 2001 From: Chris Mason Date: Sat, 30 May 2026 09:19:24 -0400 Subject: [PATCH] nfsd: cap decoded POSIX ACL count to bound sort cost nfsd4_decode_posixacl() reads a u32 entry count off the wire and passes it straight to posix_acl_alloc() and sort_pacl_range(). The latter is an O(n^2) bubble sort, so a client-chosen count drives unbounded CPU in the server's compound processing path. nfsd4_decode_posixacl() xdr_stream_decode_u32(&count) /* uncapped u32 */ posix_acl_alloc(count, GFP_KERNEL) sort_pacl_range(*acl, 0, count - 1) /* O(n^2) bubble sort */ The encoder side in the same file already rejects ACLs whose a_count exceeds NFS_ACL_MAX_ENTRIES, but the decoder introduced in commit 5fc51dfc2eb1 ("NFSD: Add support for XDR decoding POSIX draft ACLs") omitted the symmetric check. Fix by rejecting a wire count greater than NFS_ACL_MAX_ENTRIES with nfserr_inval, before any allocation, so the sort is bounded by NFS_ACL_MAX_ENTRIES^2 comparisons. While we're in here, also fix the nfserr_resource return if posix_acl_alloc() fails. That's not a legal error code for v4.1+. Change it to return nfserr_jukebox as that's more appropriate for memory allocation failures. Fixes: 5fc51dfc2eb1 ("NFSD: Add support for XDR decoding POSIX draft ACLs") Cc: stable@vger.kernel.org Assisted-by: kres:claude-opus-4-7 Reported-by: Chris Mason Signed-off-by: Chris Mason Link: https://patch.msgid.link/20260530-nfsd-fixes-v2-8-f27e8eb4d974@kernel.org Signed-off-by: Chuck Lever --- fs/nfsd/nfs4xdr.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c index e17488a911f7..09068ca61b00 100644 --- a/fs/nfsd/nfs4xdr.c +++ b/fs/nfsd/nfs4xdr.c @@ -449,9 +449,18 @@ nfsd4_decode_posixacl(struct nfsd4_compoundargs *argp, struct posix_acl **acl) if (xdr_stream_decode_u32(argp->xdr, &count) < 0) return nfserr_bad_xdr; + /* + * The NFSv4 POSIX ACL draft doesn't define a max number of ACE's, but + * the NFSACL spec does. For NFSv4, cap the number of entries to the v3 + * limit, as we want to ensure that ACLs set via NFSv4 POSIX ACL + * extensions are retrievable via NFSACL. + */ + if (count > NFS_ACL_MAX_ENTRIES) + return nfserr_inval; + *acl = posix_acl_alloc(count, GFP_KERNEL); if (*acl == NULL) - return nfserr_resource; + return nfserr_jukebox; (*acl)->a_count = count; for (ace = (*acl)->a_entries; ace < (*acl)->a_entries + count; ace++) {