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Subject[PATCH v5] kernel: make groups_sort calling a responsibility group_info allocators
Date
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@gmail.com>
---
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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