[PATCH bpf-next] bpf: test_run: Fix overflow in xdp frags bpf_test_finish

Syzkaller reports another issue:
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
check_copy_size include/linux/thread_info.h:230 [inline]
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
copy_to_user include/linux/uaccess.h:199 [inline]
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
bpf_test_finish.isra.0+0x4b2/0x680 net/bpf/test_run.c:171

This can happen when the userspace buffer is smaller than head+frags.
Return ENOSPC in this case.

Fixes: 7855e0db150a ("bpf: test_run: add xdp_shared_info pointer in bpf_test_finish signature")
Cc: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Stanislav Fomichev <redacted>
---
 net/bpf/test_run.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index f08034500813..eb129e48f90b 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c

@@ -150,6 +150,11 @@ static int bpf_test_finish(const union bpf_attr *kattr,
 	if (data_out) {
 		int len = sinfo ? copy_size - sinfo->xdp_frags_size : copy_size;
 
+		if (len < 0) {
+			err = -ENOSPC;
+			goto out;
+		}
+
 		if (copy_to_user(data_out, data, len))
 			goto out;
 

-- 
2.35.1.574.g5d30c73bfb-goog

On 3/1/22 12:23 AM, Stanislav Fomichev wrote:

Syzkaller reports another issue:
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
check_copy_size include/linux/thread_info.h:230 [inline]
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
copy_to_user include/linux/uaccess.h:199 [inline]
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
bpf_test_finish.isra.0+0x4b2/0x680 net/bpf/test_run.c:171

This can happen when the userspace buffer is smaller than head+frags.
Return ENOSPC in this case.

Fixes: 7855e0db150a ("bpf: test_run: add xdp_shared_info pointer in bpf_test_finish signature")
Cc: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Stanislav Fomichev <redacted>

Do we have a Reported-by tag for syzkaller so it can match against its report?

Thanks,
Daniel

On Tue, Mar 1, 2022 at 8:33 AM Daniel Borkmann [off-list ref] wrote:

On 3/1/22 12:23 AM, Stanislav Fomichev wrote:

quoted

Syzkaller reports another issue:
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
check_copy_size include/linux/thread_info.h:230 [inline]
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
copy_to_user include/linux/uaccess.h:199 [inline]
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
bpf_test_finish.isra.0+0x4b2/0x680 net/bpf/test_run.c:171

This can happen when the userspace buffer is smaller than head+frags.
Return ENOSPC in this case.

Fixes: 7855e0db150a ("bpf: test_run: add xdp_shared_info pointer in bpf_test_finish signature")
Cc: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Stanislav Fomichev <redacted>

Do we have a Reported-by tag for syzkaller so it can match against its report?

Oops, sorry, totally forgot:

Reported-by: syzbot+5f81df6205ecbbc56ab5@syzkaller.appspotmail.com

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Daniel Borkmann [off-list ref]:

On Mon, 28 Feb 2022 15:23:32 -0800 you wrote:

Syzkaller reports another issue:
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
check_copy_size include/linux/thread_info.h:230 [inline]
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
copy_to_user include/linux/uaccess.h:199 [inline]
WARNING: CPU: 0 PID: 10775 at include/linux/thread_info.h:230
bpf_test_finish.isra.0+0x4b2/0x680 net/bpf/test_run.c:171

[...]

Here is the summary with links:
  - [bpf-next] bpf: test_run: Fix overflow in xdp frags bpf_test_finish
    https://git.kernel.org/bpf/bpf-next/c/530e214c5b5a

You are awesome, thank you!
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