From beb4ee6770a89646659e6a2178538d2b13e2654e Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@google.com>
Date: Wed, 8 Jul 2020 13:15:20 -0700
Subject: [PATCH 1/3] Smack: fix use-after-free in smk_write_relabel_self()
smk_write_relabel_self() frees memory from the task's credentials with
no locking, which can easily cause a use-after-free because multiple
tasks can share the same credentials structure.
Fix this by using prepare_creds() and commit_creds() to correctly modify
the task's credentials.
Reproducer for "BUG: KASAN: use-after-free in smk_write_relabel_self":
#include <fcntl.h>
#include <pthread.h>
#include <unistd.h>
static void *thrproc(void *arg)
{
int fd = open("/sys/fs/smackfs/relabel-self", O_WRONLY);
for (;;) write(fd, "foo", 3);
}
int main()
{
pthread_t t;
pthread_create(&t, NULL, thrproc, NULL);
thrproc(NULL);
}
Reported-by: syzbot+e6416dabb497a650da40@syzkaller.appspotmail.com
Fixes: 38416e53936e ("Smack: limited capability for changing process label")
Cc: <stable@vger.kernel.org> # v4.4+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
security/smack/smackfs.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index c21b656b32631..840a192e93370 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -2720,7 +2720,6 @@ static int smk_open_relabel_self(struct inode *inode, struct file *file)
static ssize_t smk_write_relabel_self(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
- struct task_smack *tsp = smack_cred(current_cred());
char *data;
int rc;
LIST_HEAD(list_tmp);
@@ -2745,11 +2744,21 @@ static ssize_t smk_write_relabel_self(struct file *file, const char __user *buf,
kfree(data);
if (!rc || (rc == -EINVAL && list_empty(&list_tmp))) {
+ struct cred *new;
+ struct task_smack *tsp;
+
+ new = prepare_creds();
+ if (!new) {
+ rc = -ENOMEM;
+ goto out;
+ }
+ tsp = smack_cred(new);
smk_destroy_label_list(&tsp->smk_relabel);
list_splice(&list_tmp, &tsp->smk_relabel);
+ commit_creds(new);
return count;
}
-
+out:
smk_destroy_label_list(&list_tmp);
return rc;
}
From a6bd4f6d9b07452b0b19842044a6c3ea384b0b88 Mon Sep 17 00:00:00 2001
From: Dan Carpenter <dan.carpenter@oracle.com>
Date: Thu, 23 Jul 2020 18:22:19 +0300
Subject: [PATCH 2/3] Smack: fix another vsscanf out of bounds
This is similar to commit 84e99e58e8d1 ("Smack: slab-out-of-bounds in
vsscanf") where we added a bounds check on "rule".
Reported-by: syzbot+a22c6092d003d6fe1122@syzkaller.appspotmail.com
Fixes: f7112e6c9abf ("Smack: allow for significantly longer Smack labels v4")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
security/smack/smackfs.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index 840a192e93370..2bae1fc493d16 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -905,6 +905,10 @@ static ssize_t smk_set_cipso(struct file *file, const char __user *buf,
for (i = 0; i < catlen; i++) {
rule += SMK_DIGITLEN;
+ if (rule > data + count) {
+ rc = -EOVERFLOW;
+ goto out;
+ }
ret = sscanf(rule, "%u", &cat);
if (ret != 1 || cat > SMACK_CIPSO_MAXCATNUM)
goto out;
From 42a2df3e829f3c5562090391b33714b2e2e5ad4a Mon Sep 17 00:00:00 2001
From: Dan Carpenter <dan.carpenter@oracle.com>
Date: Thu, 23 Jul 2020 18:23:05 +0300
Subject: [PATCH 3/3] Smack: prevent underflow in smk_set_cipso()
We have an upper bound on "maplevel" but forgot to check for negative
values.
Fixes: e114e473771c ("Smack: Simplified Mandatory Access Control Kernel")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
security/smack/smackfs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index 2bae1fc493d16..9c4308077574c 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -884,7 +884,7 @@ static ssize_t smk_set_cipso(struct file *file, const char __user *buf,
}
ret = sscanf(rule, "%d", &maplevel);
- if (ret != 1 || maplevel > SMACK_CIPSO_MAXLEVEL)
+ if (ret != 1 || maplevel < 0 || maplevel > SMACK_CIPSO_MAXLEVEL)
goto out;
rule += SMK_DIGITLEN;