5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Chris Mason <redacted>
commit 6959297aaa9572783d620a226d73c3fb94494888 upstream.
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: <redacted>
Assisted-by: kres (claude-opus-4-7)
Signed-off-by: Chris Mason <redacted>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260524010213.557424-5-cel@kernel.org (local)
Signed-off-by: Chuck Lever <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sunrpc/auth_gss/gss_krb5_wrap.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
--- a/net/sunrpc/auth_gss/gss_krb5_wrap.c
+++ b/net/sunrpc/auth_gss/gss_krb5_wrap.c
@@ -389,6 +389,8 @@ static void _rotate_left(struct xdr_buf
int shifted = 0;
int this_shift;
+ if (!buf->len)
+ return;
shift %= buf->len;
while (shifted < shift) {
this_shift = min(shift - shifted, LOCAL_BUF_LEN);@@ -401,6 +403,8 @@ static void rotate_left(u32 base, struct
{
struct xdr_buf subbuf;
+ if (buf->len <= base)
+ return;
xdr_buf_subsegment(buf, &subbuf, base, buf->len - base);
_rotate_left(&subbuf, shift);
}@@ -476,6 +480,9 @@ gss_unwrap_kerberos_v2(struct krb5_ctx *
if (kctx->gk5e->decrypt_v2 == NULL)
return GSS_S_FAILURE;
+ if (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)
@@ -542,9 +549,9 @@ gss_unwrap_kerberos_v2(struct krb5_ctx *
* head buffer space rather than that actually occupied.
*/
movelen = min_t(unsigned int, buf->head[0].iov_len, 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 = len - (GSS_KRB5_TOK_HDR_LEN + headskip);