On Fri, Aug 07, 2020 at 09:13:24AM -0700, Eric Biggers wrote:
> 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(-)
Thanks for the backport, now queued up.
greg k-h
