Re: [PATCH net-next v4 2/9] net: filter: keep original BPF program around
From: Alexei Starovoitov <hidden>
Date: 2014-09-12 03:51:19
On Thu, Sep 11, 2014 at 8:27 PM, Eric Dumazet [off-list ref] wrote:
From: Eric Dumazet <edumazet@google.com> On Fri, 2014-03-28 at 18:58 +0100, Daniel Borkmann wrote:quoted
In order to open up the possibility to internally transform a BPF program into an alternative and possibly non-trivial reversible representation, we need to keep the original BPF program around, so that it can be passed back to user space w/o the need of a complex decoder. The reason for that use case resides in commit a8fc92778080 ("sk-filter: Add ability to get socket filter program (v2)"), that is, the ability to retrieve the currently attached BPF filter from a given socket used mainly by the checkpoint-restore project, for example. Therefore, we add two helpers sk_{store,release}_orig_filter for taking care of that. In the sk_unattached_filter_create() case, there's no such possibility/requirement to retrieve a loaded BPF program. Therefore, we can spare us the work in that case. This approach will simplify and slightly speed up both, sk_get_filter() and sock_diag_put_filterinfo() handlers as we won't need to successively decode filters anymore through sk_decode_filter(). As we still need sk_decode_filter() later on, we're keeping it around. Joint work with Alexei Starovoitov. Signed-off-by: Alexei Starovoitov <redacted> Signed-off-by: Daniel Borkmann <redacted> Cc: Pavel Emelyanov <redacted> ---Note that this patch added a possible use after free. Following patch should be sent to stable trees only, as 3.17+ incidentally fixed this with commit 278571baca2aecf5fb5cb5c8b002dbfa0a6c524c net: filter: simplify socket charging [PATCH] net: filter: fix possible use after free If kmemdup() fails, we free fp->orig_prog and return -ENOMEM sk_attach_filter() -> sk_filter_uncharge(sk, fp) -> sk_filter_release(fp) -> call_rcu(&fp->rcu, sk_filter_release_rcu) -> sk_filter_release_rcu() -> sk_release_orig_filter() fprog = fp->orig_prog; // not NULL, but points to freed memory kfree(fprog->filter); // use after free, potential corruption kfree(fprog); // double free or corruption Note: This was fixed in 3.17+ with commit 278571baca2a ("net: filter: simplify socket charging") Found by AddressSanitizer Signed-off-by: Eric Dumazet <edumazet@google.com> Fixes: a3ea269b8bcdb ("net: filter: keep original BPF program around")
Wow. that's a tricky one. Thanks! Acked-by: Alexei Starovoitov <redacted> Indeed 3.17 is ok, but the fix is small enough, so wouldn't hurt to apply it everywhere. Just for consistency?
quoted hunk ↗ jump to hunk
---diff --git a/net/core/filter.c b/net/core/filter.c index 1dbf6462f766..3139f966a178 100644 --- a/net/core/filter.c +++ b/net/core/filter.c@@ -1318,6 +1318,7 @@ static int sk_store_orig_filter(struct sk_filter *fp, fkprog->filter = kmemdup(fp->insns, fsize, GFP_KERNEL); if (!fkprog->filter) { kfree(fp->orig_prog); + fp->orig_prog = NULL; return -ENOMEM; }