The branch stable/14 has been updated by olce: URL: https://cgit.FreeBSD.org/src/commit/?id=0574fca39fb3fa8fef062b74e82f359b99f1bee0
commit 0574fca39fb3fa8fef062b74e82f359b99f1bee0 Author: Olivier Certner <[email protected]> AuthorDate: 2025-10-07 10:02:23 +0000 Commit: Olivier Certner <[email protected]> CommitDate: 2025-12-19 09:16:44 +0000 sys/rpc: UNIX auth: Fix OOB accesses, notably writes on decode When the received authentication message had more than XU_NGROUPS, we would write group IDs beyond the end of cr_groups[] in the 'struct xucred' being filled (as 'ngroups_max' is always greater than XU_NGROUPS). For robustness, prevent various OOB accesses that would result from a change of value of XU_NGROUPS or a 'struct xucred' with an invalid 'cr_ngroups' field, even if these cases are unlikely. Reviewed by: rmacklem Fixes: dfdcada31e79 ("Add the new kernel-mode NFS Lock Manager.") MFC after: 2 days Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D52960 (cherry picked from commit 47e9c81d4f1324674c624df02a51ad3a72aa7444) --- sys/rpc/authunix_prot.c | 40 +++++++++++++++++++++------------------- 1 file changed, 21 insertions(+), 19 deletions(-) diff --git a/sys/rpc/authunix_prot.c b/sys/rpc/authunix_prot.c index 42822a5d01c6..f2749e68e763 100644 --- a/sys/rpc/authunix_prot.c +++ b/sys/rpc/authunix_prot.c @@ -79,7 +79,6 @@ xdr_authunix_parms(XDR *xdrs, uint32_t *time, struct xucred *cred) } else { namelen = 0; } - junk = 0; if (!xdr_uint32_t(xdrs, time) || !xdr_uint32_t(xdrs, &namelen)) @@ -97,15 +96,25 @@ xdr_authunix_parms(XDR *xdrs, uint32_t *time, struct xucred *cred) if (!xdr_uint32_t(xdrs, &cred->cr_uid)) return (FALSE); + + /* + * Safety check: The protocol needs at least one group (access to + * 'cr_gid', decrementation of 'cr_ngroups' below). + */ + if (xdrs->x_op == XDR_ENCODE && cred->cr_ngroups == 0) + return (FALSE); if (!xdr_uint32_t(xdrs, &cred->cr_gid)) return (FALSE); if (xdrs->x_op == XDR_ENCODE) { /* - * Note that this is a `struct xucred`, which maintains its - * historical layout of preserving the egid in cr_ngroups and - * cr_groups[0] == egid. + * Note that this is a 'struct xucred', which still has the + * historical layout where the effective GID is in cr_groups[0] + * and is accounted in 'cr_ngroups'. We substract 1 to obtain + * the number of "supplementary" groups, passed in the AUTH_SYS + * credentials variable-length array called gids[] in RFC 5531. */ + MPASS(cred->cr_ngroups <= XU_NGROUPS); supp_ngroups = cred->cr_ngroups - 1; if (supp_ngroups > NGRPS) supp_ngroups = NGRPS; @@ -113,22 +122,15 @@ xdr_authunix_parms(XDR *xdrs, uint32_t *time, struct xucred *cred) if (!xdr_uint32_t(xdrs, &supp_ngroups)) return (FALSE); - for (i = 0; i < supp_ngroups; i++) { - if (i < ngroups_max) { - if (!xdr_uint32_t(xdrs, &cred->cr_groups[i + 1])) - return (FALSE); - } else { - if (!xdr_uint32_t(xdrs, &junk)) - return (FALSE); - } - } - if (xdrs->x_op == XDR_DECODE) { - if (supp_ngroups > ngroups_max) - cred->cr_ngroups = ngroups_max + 1; - else - cred->cr_ngroups = supp_ngroups + 1; - } + junk = 0; + for (i = 0; i < supp_ngroups; ++i) + if (!xdr_uint32_t(xdrs, i < XU_NGROUPS - 1 ? + &cred->cr_groups[i + 1] : &junk)) + return (FALSE); + + if (xdrs->x_op != XDR_ENCODE) + cred->cr_ngroups = MIN(supp_ngroups + 1, XU_NGROUPS); return (TRUE); }
