[PATCH bpf-next] bpf: bpf_prog_pack: set proper size before freeing ro_header

[PATCH bpf-next] bpf: bpf_prog_pack: set proper size before freeing ro_header

[Song Liu]

bpf_prog_pack_free() uses header->size to decide whether the header
should be freed with module_memfree() or the bpf_prog_pack logic.
However, in kvmalloc() failure path of bpf_jit_binary_pack_alloc(),
header->size is not set yet. As a result, bpf_prog_pack_free() may treat
a slice of a pack as a standalone kvmalloc'd header and call
module_memfree() on the whole pack. This in turn causes use-after-free by
other users of the pack.

Fix this by setting ro_header->size before freeing ro_header.

Fixes: 33c9805860e5 ("bpf: Introduce bpf_jit_binary_pack_[alloc|finalize|free]")
Reported-by: syzbot+2f649ec6d2eea1495a8f@syzkaller.appspotmail.com
Reported-by: syzbot+ecb1e7e51c52f68f7481@syzkaller.appspotmail.com
Reported-by: syzbot+87f65c75f4a72db05445@syzkaller.appspotmail.com
Signed-off-by: Song Liu <song@kernel.org>
---
 kernel/bpf/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 44623c9b5bb1..ebb0193d07f0 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1069,6 +1069,7 @@ bpf_jit_binary_pack_alloc(unsigned int proglen, u8 **image_ptr,
 
 	*rw_header = kvmalloc(size, GFP_KERNEL);
 	if (!*rw_header) {
+		bpf_arch_text_copy(&ro_header->size, &size, sizeof(size));
 		bpf_prog_pack_free(ro_header);
 		bpf_jit_uncharge_modmem(size);
 		return NULL;
-- 
2.30.2

Re: [PATCH bpf-next] bpf: bpf_prog_pack: set proper size before freeing ro_header

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Thu, 17 Feb 2022 10:30:01 -0800 you wrote:
> bpf_prog_pack_free() uses header->size to decide whether the header
> should be freed with module_memfree() or the bpf_prog_pack logic.
> However, in kvmalloc() failure path of bpf_jit_binary_pack_alloc(),
> header->size is not set yet. As a result, bpf_prog_pack_free() may treat
> a slice of a pack as a standalone kvmalloc'd header and call
> module_memfree() on the whole pack. This in turn causes use-after-free by
> other users of the pack.
> 
> [...]

Here is the summary with links:
  - [bpf-next] bpf: bpf_prog_pack: set proper size before freeing ro_header
    https://git.kernel.org/bpf/bpf-next/c/d24d2a2b0a81

You are awesome, thank you!
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