CVE-2026-89541

In the Linux kernel, the following vulnerability has been resolved:

SUNRPC: harden gss_unwrap_resp_priv length checks

gss_unwrap_resp_priv() validates the RPCSEC_GSS opaque length with

offset = (u8 *)(p) - (u8 *)head->iov_base;
if (offset + opaque_len > rcv_buf->len)
        goto unwrap_failed;
maj_stat = gss_unwrap(ctx->gc_gss_ctx, offset,
                      offset + opaque_len, rcv_buf);

Both operands are u32 and the sum is computed in u32. A reply with opaque_len near 0xffffffff makes offset + opaque_len wrap to a small value that is below rcv_buf->len, so the bound check passes and gss_unwrap() is called with end < begin. The check also lacks a lower bound, so any opaque_len in [0, GSS_KRB5_TOK_HDR_LEN) is accepted and forwarded to gss_krb5_unwrap_v2(), whose pre-decrypt header reads at ptr+4 and ptr+6 then run past the token.

A krb5p NFS server returning a crafted RPCSEC_GSS reply can drive the client into out-of-bounds reads in gss_krb5_unwrap_v2() and the rotate_left() loop that follows.

Fix by replacing the single combined check with three guards that are safe in u32 arithmetic and that enforce the RFC 4121 minimum outer token length:

if (offset > rcv_buf->len)
        goto unwrap_failed;
if (opaque_len > rcv_buf->len - offset)
        goto unwrap_failed;
if (opaque_len < GSS_KRB5_TOK_HDR_LEN)
        goto unwrap_failed;

The first guard makes the subtraction in the second guard unconditionally safe; offset is derived from a successful xdr_inline_decode() in the head kvec, so in practice it already satisfies the bound. The floor mirrors the server-side check added in commit 5b757c2e57a5 (SUNRPC: svcauth_gss: enforce krb5 token minimum length).

Affected Software

References

• https://git.kernel.org/stable/c/3691c4b3488d8ca046b9941e5be30c626dbbbb50
• https://git.kernel.org/stable/c/401f6a5b338d05bb1069ad814d9f77e3c367854f
• https://git.kernel.org/stable/c/81fd7654a8429718adfcb2a7e03496077f547ed0
• https://git.kernel.org/stable/c/85fa6b12e8f439739ac36ef2aad925f37c8b976a
• https://git.kernel.org/stable/c/87831b92112c81db251d46756d65daa4f91af6a2
• https://git.kernel.org/stable/c/89a15a50f84d32d4b99db86f957427fcbe20a99a
• https://git.kernel.org/stable/c/d395c30d570ca6168f0297b191709927d1258273
• https://git.kernel.org/stable/c/ebcbd2523a8524c3d24e111cdbed8e271d910269