From: Jeff Layton <jlayton@kernel.org> stable inclusion from stable-v5.10.270 commit 3a7fd224df0fbb42167eb1b77be45d72fe0b1098 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/18937 CVE: CVE-2026-89674 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- commit f9868174af49d207fbaf0c5e055d088a983684af upstream. The XDR buffer size calculation in nfsd4_ff_encode_layoutget() has multiple errors that can result in either an out-of-bounds write or leaking uninitialized kernel memory to the client: - fh_len doesn't account for XDR padding on the file handle data - uid and gid lengths use "8 + len" but xdr_encode_opaque() actually writes "4 + xdr_align_size(len)" bytes - ds_len omits the flags and stats_collect_hint fields (8 bytes), while len's header constant overestimates by 8 bytes -- these partially cancel but leave a net mismatch The worst case occurs with short strings (e.g. uid=0, gid=0 with an odd-sized file handle), where the function writes up to 5 bytes past the reserved XDR buffer. Conversely, when string lengths happen to be 4-byte aligned, the reservation is too large and stale buffer content is sent to the client. Fix this by breaking out every encoded field explicitly in the ds_len calculation, using xdr_align_size() for all variable-length opaque fields, and correcting the header constants. Fixes: 9b9960a0ca47 ("nfsd: Add a super simple flex file server") Cc: stable@vger.kernel.org Assisted-by: kres:claude-opus-4-7 Signed-off-by: Jeff Layton <jlayton@kernel.org> Link: https://patch.msgid.link/20260528-pnfs-fixes-v1-1-8a1255ae2f16@kernel.org Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Cai Xinchen <caixinchen1@huawei.com> --- fs/nfsd/flexfilelayoutxdr.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) diff --git a/fs/nfsd/flexfilelayoutxdr.c b/fs/nfsd/flexfilelayoutxdr.c index e81d2a5cf381..f9aaf3dc3e71 100644 --- a/fs/nfsd/flexfilelayoutxdr.c +++ b/fs/nfsd/flexfilelayoutxdr.c @@ -30,19 +30,24 @@ nfsd4_ff_encode_layoutget(struct xdr_stream *xdr, struct ff_idmap uid; struct ff_idmap gid; - fh_len = 4 + fl->fh.size; + fh_len = 4 + xdr_align_size(fl->fh.size); uid.len = sprintf(uid.buf, "%u", from_kuid(&init_user_ns, fl->uid)); gid.len = sprintf(gid.buf, "%u", from_kgid(&init_user_ns, fl->gid)); - /* 8 + len for recording the length, name, and padding */ - ds_len = 20 + sizeof(stateid_opaque_t) + 4 + fh_len + - 8 + uid.len + 8 + gid.len; + /* data server entry: deviceid + efficiency + stateid + fh list + + * user + group + flags + stats_collect_hint + */ + ds_len = 16 + 4 + 4 + sizeof(stateid_opaque_t) + 4 + fh_len + + 4 + xdr_align_size(uid.len) + + 4 + xdr_align_size(gid.len) + + 4 + 4; + /* mirror: ds_count + ds */ mirror_len = 4 + ds_len; - /* The layout segment */ - len = 20 + mirror_len; + /* stripe_unit + mirror_count + mirror */ + len = 12 + mirror_len; p = xdr_reserve_space(xdr, sizeof(__be32) + len); if (!p) -- 2.34.1