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[v3,bpf-next,1/7] bpf: Reject indirect var_off stack access in raw mode

Message ID 7c56c0ea7c0e59664d2566fd419c6cb7ea3efc3c.1554358433.git.rdna@fb.com
State Accepted
Delegated to: BPF Maintainers
Headers show
Series bpf: Fix indirect var_off stack access support | expand

Commit Message

Andrey Ignatov April 4, 2019, 6:22 a.m. UTC 
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>
---
 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 0fd4946387bb..e9c093e632f2 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2226,6 +2226,15 @@  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,