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Date: Tue, 12 Dec 2017 08:43:58 +1100
From: NeilBrown <neilb@...e.com>
To: David Howells <dhowells@...hat.com>
Cc: linux-nfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org,
Thiago Rafael Becker <thiago.becker@...il.com>
Subject: Re: [PATCH v5] kernel: make groups_sort calling a responsibility group_info allocators
On Mon, Dec 11 2017, Thiago Rafael Becker wrote:
> In testing, we found that nfsd threads may call set_groups in parallel for
> the same entry cached in auth.unix.gid, racing in the call of groups_sort,
> corrupting the groups for that entry and leading to permission denials for
> the client.
>
> This patch:
> - Make groups_sort globally visible.
> - Move the call to groups_sort to the modifiers of group_info
> - Remove the call to groups_sort from set_groups
>
> Signed-off-by: Thiago Rafael Becker <thiago.becker@...il.com>
Reviewed-by: NeilBrown <neilb@...e.com>
Thanks. I like this better as a single patch.
I'd probably suggest "Cc: stable@...r.kernel.org".
Less important bugfixes have gone to stable...
It might be nice to enhance
Documentation/security/credentials.rst
to explain that the groups list is always sorted, and must be sorted
before set_groups() or set_current_groups() is called, but
as the document doesn't mention any of this at all, this is purely
an extra enhancement and doesn't need to be included in the same patch.
David: do you agree that this sort of content would be appropriate in
that file (which you apparently authored). Would you like to update it,
or shall I?
Thanks,
NeilBrown
> ---
> arch/s390/kernel/compat_linux.c | 1 +
> fs/nfsd/auth.c | 3 +++
> include/linux/cred.h | 1 +
> kernel/groups.c | 5 +++--
> kernel/uid16.c | 1 +
> net/sunrpc/auth_gss/gss_rpc_xdr.c | 1 +
> net/sunrpc/auth_gss/svcauth_gss.c | 1 +
> net/sunrpc/svcauth_unix.c | 2 ++
> 8 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/kernel/compat_linux.c b/arch/s390/kernel/compat_linux.c
> index f04db37..59eea9c 100644
> --- a/arch/s390/kernel/compat_linux.c
> +++ b/arch/s390/kernel/compat_linux.c
> @@ -263,6 +263,7 @@ COMPAT_SYSCALL_DEFINE2(s390_setgroups16, int, gidsetsize, u16 __user *, grouplis
> return retval;
> }
>
> + groups_sort(group_info);
> retval = set_current_groups(group_info);
> put_group_info(group_info);
>
> diff --git a/fs/nfsd/auth.c b/fs/nfsd/auth.c
> index 697f8ae..f650e47 100644
> --- a/fs/nfsd/auth.c
> +++ b/fs/nfsd/auth.c
> @@ -60,6 +60,9 @@ int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export *exp)
> gi->gid[i] = exp->ex_anon_gid;
> else
> gi->gid[i] = rqgi->gid[i];
> +
> + /* Each thread allocates its own gi, no race */
> + groups_sort(gi);
> }
> } else {
> gi = get_group_info(rqgi);
> diff --git a/include/linux/cred.h b/include/linux/cred.h
> index 099058e..6312865 100644
> --- a/include/linux/cred.h
> +++ b/include/linux/cred.h
> @@ -83,6 +83,7 @@ extern int set_current_groups(struct group_info *);
> extern void set_groups(struct cred *, struct group_info *);
> extern int groups_search(const struct group_info *, kgid_t);
> extern bool may_setgroups(void);
> +extern void groups_sort(struct group_info *);
>
> /*
> * The security context of a task
> diff --git a/kernel/groups.c b/kernel/groups.c
> index e357bc8..daae2f2 100644
> --- a/kernel/groups.c
> +++ b/kernel/groups.c
> @@ -86,11 +86,12 @@ static int gid_cmp(const void *_a, const void *_b)
> return gid_gt(a, b) - gid_lt(a, b);
> }
>
> -static void groups_sort(struct group_info *group_info)
> +void groups_sort(struct group_info *group_info)
> {
> sort(group_info->gid, group_info->ngroups, sizeof(*group_info->gid),
> gid_cmp, NULL);
> }
> +EXPORT_SYMBOL(groups_sort);
>
> /* a simple bsearch */
> int groups_search(const struct group_info *group_info, kgid_t grp)
> @@ -122,7 +123,6 @@ int groups_search(const struct group_info *group_info, kgid_t grp)
> void set_groups(struct cred *new, struct group_info *group_info)
> {
> put_group_info(new->group_info);
> - groups_sort(group_info);
> get_group_info(group_info);
> new->group_info = group_info;
> }
> @@ -206,6 +206,7 @@ SYSCALL_DEFINE2(setgroups, int, gidsetsize, gid_t __user *, grouplist)
> return retval;
> }
>
> + groups_sort(group_info);
> retval = set_current_groups(group_info);
> put_group_info(group_info);
>
> diff --git a/kernel/uid16.c b/kernel/uid16.c
> index ce74a49..ef1da2a 100644
> --- a/kernel/uid16.c
> +++ b/kernel/uid16.c
> @@ -192,6 +192,7 @@ SYSCALL_DEFINE2(setgroups16, int, gidsetsize, old_gid_t __user *, grouplist)
> return retval;
> }
>
> + groups_sort(group_info);
> retval = set_current_groups(group_info);
> put_group_info(group_info);
>
> diff --git a/net/sunrpc/auth_gss/gss_rpc_xdr.c b/net/sunrpc/auth_gss/gss_rpc_xdr.c
> index c4778ca..444380f 100644
> --- a/net/sunrpc/auth_gss/gss_rpc_xdr.c
> +++ b/net/sunrpc/auth_gss/gss_rpc_xdr.c
> @@ -231,6 +231,7 @@ static int gssx_dec_linux_creds(struct xdr_stream *xdr,
> goto out_free_groups;
> creds->cr_group_info->gid[i] = kgid;
> }
> + groups_sort(creds->cr_group_info);
>
> return 0;
> out_free_groups:
> diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
> index 5dd4e6c..2653119 100644
> --- a/net/sunrpc/auth_gss/svcauth_gss.c
> +++ b/net/sunrpc/auth_gss/svcauth_gss.c
> @@ -481,6 +481,7 @@ static int rsc_parse(struct cache_detail *cd,
> goto out;
> rsci.cred.cr_group_info->gid[i] = kgid;
> }
> + groups_sort(rsci.cred.cr_group_info);
>
> /* mech name */
> len = qword_get(&mesg, buf, mlen);
> diff --git a/net/sunrpc/svcauth_unix.c b/net/sunrpc/svcauth_unix.c
> index 740b67d..af7f28f 100644
> --- a/net/sunrpc/svcauth_unix.c
> +++ b/net/sunrpc/svcauth_unix.c
> @@ -520,6 +520,7 @@ static int unix_gid_parse(struct cache_detail *cd,
> ug.gi->gid[i] = kgid;
> }
>
> + groups_sort(ug.gi);
> ugp = unix_gid_lookup(cd, uid);
> if (ugp) {
> struct cache_head *ch;
> @@ -819,6 +820,7 @@ svcauth_unix_accept(struct svc_rqst *rqstp, __be32 *authp)
> kgid_t kgid = make_kgid(&init_user_ns, svc_getnl(argv));
> cred->cr_group_info->gid[i] = kgid;
> }
> + groups_sort(cred->cr_group_info);
> if (svc_getu32(argv) != htonl(RPC_AUTH_NULL) || svc_getu32(argv) != 0) {
> *authp = rpc_autherr_badverf;
> return SVC_DENIED;
> --
> 2.9.5
>
> --
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