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bpf/verifier: allow all functions to read user provided context

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When a function was trying to access data from context in a syscall eBPF
program, the verifier was rejecting the call unless it was accessing the
first element.
This is because the syscall context is not known at compile time, and
so we need to check this when actually accessing it.

Check for the valid memory access if there is no convert_ctx callback,
and allow such situation to happen.

Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Link: https://lore.kernel.org/r/20220906151303.2780789-4-benjamin.tissoires@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Benjamin Tissoires 2022-09-06 17:12:59 +02:00 committed by Alexei Starovoitov
parent 95f2f26f3c
commit 15baa55ff5
1 changed files with 19 additions and 0 deletions
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19
kernel/bpf/verifier.c
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@ -5233,6 +5233,25 @@ static int check_helper_mem_access(struct bpf_verifier_env *env, int regno,
env,
regno, reg->off, access_size,
zero_size_allowed, ACCESS_HELPER, meta);
case PTR_TO_CTX:
/* in case the function doesn't know how to access the context,
* (because we are in a program of type SYSCALL for example), we
* can not statically check its size.
* Dynamically check it now.
*/
if (!env->ops->convert_ctx_access) {
enum bpf_access_type atype = meta && meta->raw_mode ? BPF_WRITE : BPF_READ;
int offset = access_size - 1;
/* Allow zero-byte read from PTR_TO_CTX */
if (access_size == 0)
return zero_size_allowed ? 0 : -EACCES;
return check_mem_access(env, env->insn_idx, regno, offset, BPF_B,
atype, -1, false);
}
fallthrough;
default: /* scalar_value or invalid ptr */
/* Allow zero-byte read from NULL, regardless of pointer type */
if (zero_size_allowed && access_size == 0 &&