Smack: fix use-after-free in smk_write_relabel_self()
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: [email protected]
Fixes: 38416e53936e ("Smack: limited capability for changing process label")
Cc: <[email protected]> # v4.4+
Signed-off-by: Eric Biggers <[email protected]>
Signed-off-by: Casey Schaufler <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
1 file changed