On 5/1/23 9:55 AM, Stanislav Fomichev wrote:
On Sun, Apr 30, 2023 at 10:52 PM Martin KaFai Lau <martin.lau@xxxxxxxxx> wrote:
On 4/27/23 1:04 PM, Stanislav Fomichev wrote:
@@ -1881,8 +1886,10 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level,
.optname = optname,
.current_task = current,
};
+ int orig_optlen;
int ret;
+ orig_optlen = max_optlen;
For getsockopt, when the kernel's getsockopt finished successfully (the
following 'if (!retval)' case), how about also setting orig_optlen to the kernel
returned 'optlen'. For example, the user's orig_optlen is 8096 and the kernel
returned optlen is 1024. If the bpf prog still sets the ctx.optlen to something
> PAGE_SIZE, -EFAULT will be returned.
Wouldn't it defeat the purpose? Or am I missing something?
ctx.optlen would still be 8096, not 1024, right (regardless of what
the kernel returns)?
So it would trigger EFAULT case which we try to avoid.
My understanding is the ctx.optlen should be 1024 after the 'if (!retval)'
statement.
The 'int __user *optlen' arg has the kernel returned optlen (1024). The 'int
max_optlen' arg has the original user's optlen (8096).
int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level,
int optname, char __user *optval,
int __user *optlen /* 1024 */,
int max_optlen /* 8096 */,
int retval)
{
/* ... */
orig_optlen = max_optlen; /* orig_optlen == 8096 */
ctx.optlen = max_optlen; /* ctx.optlen == 8096 */
if (!retval) {
/* If kernel getsockopt finished successfully,
* copy whatever was returned to the user back
* into our temporary buffer. Set optlen to the
* one that kernel returned as well to let
* BPF programs inspect the value.
*/
if (get_user(ctx.optlen, optlen)) {
ret = -EFAULT;
goto out;
}
/* ctx.optlen == 1024 */
orig_optlen = ctx.optlen;
}
/* ... */
}
