From: Chris Mason <clm@meta.com> mainline inclusion from mainline-v7.3-rc1 commit 6959297aaa9572783d620a226d73c3fb94494888 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/18878 CVE: CVE-2026-89542 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- gss_krb5_unwrap_v2() reads the EC and RRC header fields at ptr+4 and ptr+6 before validating that the token is at least GSS_KRB5_TOK_HDR_LEN (16) bytes long, and its rotate_left() helper passes buf->len - base to xdr_buf_subsegment() without verifying that base <= buf->len. When a caller hands in a sub-16-byte token, or a token whose declared len leaves base past the end of the buffer, three distinct failures follow: gss_krb5_unwrap_v2(offset, len, buf) ptr = buf->head[0].iov_base + offset ec = *(ptr + 4) /* OOB read on short head */ rrc = *(ptr + 6) /* OOB read on short head */ rotate_left(offset + 16, buf, rrc) xdr_buf_subsegment(buf, &subbuf, base, buf->len - base) /* u32 wrap when base > len */ _rotate_left(&subbuf, shift) shift %= buf->len /* divide-by-zero when base == len */ After decryption, the cleanup arithmetic has the same shape: movelen = min_t(unsigned int, buf->head[0].iov_len, len); movelen -= offset + GSS_KRB5_TOK_HDR_LEN + headskip; BUG_ON(offset + GSS_KRB5_TOK_HDR_LEN + headskip + movelen > buf->head[0].iov_len); The BUG_ON re-adds the value just subtracted, so it reduces to min(A, B) > A and is permanently false; it cannot catch the unsigned underflow of movelen, which then drives a ~UINT_MAX-byte memmove(). Add four defense-in-depth guards inside the unwrap core so it is safe regardless of what its callers validate: - reject tokens with len - offset < GSS_KRB5_TOK_HDR_LEN before touching ptr+4/ptr+6; - bail from rotate_left() when buf->len <= base, covering both the underflow and zero-length cases; - return early from _rotate_left() when buf->len is zero, so the shift %= buf->len modulo cannot fault; - replace the dead BUG_ON with a live check that returns GSS_S_DEFECTIVE_TOKEN before the movelen subtraction. Fixes: de9c17eb4a91 ("gss_krb5: add support for new token formats in rfc4121") Cc: stable@vger.kernel.org Assisted-by: kres (claude-opus-4-7) Signed-off-by: Chris Mason <clm@meta.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> Link: https://patch.msgid.link/20260524010213.557424-5-cel@kernel.org Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Conflicts: net/sunrpc/auth_gss/gss_krb5_wrap.c [commit e01b2c79f4af is not backport] Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com> --- net/sunrpc/auth_gss/gss_krb5_wrap.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/net/sunrpc/auth_gss/gss_krb5_wrap.c b/net/sunrpc/auth_gss/gss_krb5_wrap.c index b85899bf9d79..33debe19cfa4 100644 --- a/net/sunrpc/auth_gss/gss_krb5_wrap.c +++ b/net/sunrpc/auth_gss/gss_krb5_wrap.c @@ -420,6 +420,8 @@ static void _rotate_left(struct xdr_buf *buf, unsigned int shift) int shifted = 0; int this_shift; + if (!buf->len) + return; shift %= buf->len; while (shifted < shift) { this_shift = min(shift - shifted, LOCAL_BUF_LEN); @@ -432,6 +434,8 @@ static void rotate_left(u32 base, struct xdr_buf *buf, unsigned int shift) { struct xdr_buf subbuf; + if (buf->len <= base) + return; xdr_buf_subsegment(buf, &subbuf, base, buf->len - base); _rotate_left(&subbuf, shift); } @@ -507,6 +511,9 @@ gss_unwrap_kerberos_v2(struct krb5_ctx *kctx, int offset, struct xdr_buf *buf) if (kctx->gk5e->decrypt_v2 == NULL) return GSS_S_FAILURE; + if (buf->len - offset <= GSS_KRB5_TOK_HDR_LEN) + return GSS_S_DEFECTIVE_TOKEN; + ptr = buf->head[0].iov_base + offset; if (be16_to_cpu(*((__be16 *)ptr)) != KG2_TOK_WRAP) @@ -573,9 +580,9 @@ gss_unwrap_kerberos_v2(struct krb5_ctx *kctx, int offset, struct xdr_buf *buf) * head buffer space rather than that actually occupied. */ movelen = min_t(unsigned int, buf->head[0].iov_len, buf->len); + if (movelen < offset + GSS_KRB5_TOK_HDR_LEN + headskip) + return GSS_S_DEFECTIVE_TOKEN; movelen -= offset + GSS_KRB5_TOK_HDR_LEN + headskip; - BUG_ON(offset + GSS_KRB5_TOK_HDR_LEN + headskip + movelen > - buf->head[0].iov_len); memmove(ptr, ptr + GSS_KRB5_TOK_HDR_LEN + headskip, movelen); buf->head[0].iov_len -= GSS_KRB5_TOK_HDR_LEN + headskip; buf->len -= GSS_KRB5_TOK_HDR_LEN + headskip; -- 2.43.0