From: Eric Biggers <ebiggers@xxxxxxxxxx>
commit beb4ee6770a89646659e6a2178538d2b13e2654e upstream.
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@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 38416e53936e ("Smack: limited capability for changing process label")
Cc: <stable@xxxxxxxxxxxxxxx> # v4.4+
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
---
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 371ae368da35..10ee51d04492 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -2746,7 +2746,6 @@ 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 = current_security();
char *data;
int rc;
LIST_HEAD(list_tmp);
@@ -2771,11 +2770,21 @@ 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 = new->security;
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;
}
--
2.28.0.236.gb10cc79966-goog
