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[4.19,04/13] bpf: Reject indirect var_off stack access in raw mode

Message ID 20210913153537.2162465-5-ovidiu.panait@windriver.com
State New
Headers show
Series [4.19,01/13] bpf/verifier: per-register parent pointers | expand

Commit Message

Ovidiu Panait Sept. 13, 2021, 3:35 p.m. UTC 
From: Andrey Ignatov <rdna@fb.com>

commit f2bcd05ec7b839ff826d2008506ad2d2dff46a59 upstream.

It's hard to guarantee that whole memory is marked as initialized on
helper return if uninitialized stack is accessed with variable offset
since specific bounds are unknown to verifier. This may cause
uninitialized stack leaking.

Reject such an access in check_stack_boundary to prevent possible
leaking.

There are no known use-cases for indirect uninitialized stack access
with variable offset so it shouldn't break anything.

Fixes: 2011fccfb61b ("bpf: Support variable offset stack access from helpers")
Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
---
 kernel/bpf/verifier.c | 9 +++++++++
 1 file changed, 9 insertions(+)
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Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 47395fa40219..a5360b603e4c 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1811,6 +1811,15 @@  static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
 		if (err)
 			return err;
 	} else {
+		/* Only initialized buffer on stack is allowed to be accessed
+		 * with variable offset. With uninitialized buffer it's hard to
+		 * guarantee that whole memory is marked as initialized on
+		 * helper return since specific bounds are unknown what may
+		 * cause uninitialized stack leaking.
+		 */
+		if (meta && meta->raw_mode)
+			meta = NULL;
+
 		min_off = reg->smin_value + reg->off;
 		max_off = reg->umax_value + reg->off;
 		err = __check_stack_boundary(env, regno, min_off, access_size,