[PATCH bpf v2] bpf: don't leak memory in bpf getsockopt when optlen == 0

optlen == 0 indicates that the kernel should ignore BPF buffer
and use the original one from the user. We, however, forget
to free the temporary buffer that we've allocated for BPF.

Reported-by: Martin KaFai Lau <redacted>
Fixes: d8fe449a9c51 ("bpf: Don't return EINVAL from {get,set}sockopt when optlen > PAGE_SIZE")
Signed-off-by: Stanislav Fomichev <redacted>
---
 kernel/bpf/cgroup.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 6ec088a96302..96555a8a2c54 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c

@@ -1391,12 +1391,13 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level,
 		if (ctx.optlen != 0) {
 			*optlen = ctx.optlen;
 			*kernel_optval = ctx.optval;
+			/* export and don't free sockopt buf */
+			return 0;
 		}
 	}
 
 out:
-	if (ret)
-		sockopt_free_buf(&ctx);
+	sockopt_free_buf(&ctx);
 	return ret;
 }
 

-- 
2.30.0.284.gd98b1dd5eaa7-goog

On Tue, Jan 12, 2021 at 08:28:29AM -0800, Stanislav Fomichev wrote:

optlen == 0 indicates that the kernel should ignore BPF buffer
and use the original one from the user. We, however, forget
to free the temporary buffer that we've allocated for BPF.

Acked-by: Martin KaFai Lau <redacted>

Hello:

This patch was applied to bpf/bpf.git (refs/heads/master):

On Tue, 12 Jan 2021 08:28:29 -0800 you wrote:

optlen == 0 indicates that the kernel should ignore BPF buffer
and use the original one from the user. We, however, forget
to free the temporary buffer that we've allocated for BPF.

Reported-by: Martin KaFai Lau <redacted>
Fixes: d8fe449a9c51 ("bpf: Don't return EINVAL from {get,set}sockopt when optlen > PAGE_SIZE")
Signed-off-by: Stanislav Fomichev <redacted>

[...]

Here is the summary with links:
  - [bpf,v2] bpf: don't leak memory in bpf getsockopt when optlen == 0
    https://git.kernel.org/bpf/bpf/c/4be34f3d0731

You are awesome, thank you!
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