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bpf: Add MEM_RDONLY for helper args that are pointers to rdonly mem.

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commit 216e3cd2f28dbbf1fe86848e0e29e6693b9f0a20 upstream.

Some helper functions may modify its arguments, for example,
bpf_d_path, bpf_get_stack etc. Previously, their argument types
were marked as ARG_PTR_TO_MEM, which is compatible with read-only
mem types, such as PTR_TO_RDONLY_BUF. Therefore it's legitimate,
but technically incorrect, to modify a read-only memory by passing
it into one of such helper functions.

This patch tags the bpf_args compatible with immutable memory with
MEM_RDONLY flag. The arguments that don't have this flag will be
only compatible with mutable memory types, preventing the helper
from modifying a read-only memory. The bpf_args that have
MEM_RDONLY are compatible with both mutable memory and immutable
memory.

Signed-off-by: Hao Luo <haoluo@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211217003152.48334-9-haoluo@google.com
Cc: stable@vger.kernel.org # 5.15.x
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Hao Luo
2022-04-28 16:57:49 -07:00
committed by Greg Kroah-Hartman
parent 15166bb300
commit 2a77c58726
9 changed files with 71 additions and 55 deletions
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4
include/linux/bpf.h
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@@ -307,7 +307,9 @@ enum bpf_type_flag {
/* PTR may be NULL. */
PTR_MAYBE_NULL = BIT(0 + BPF_BASE_TYPE_BITS),
/* MEM is read-only. */
/* MEM is read-only. When applied on bpf_arg, it indicates the arg is
* compatible with both mutable and immutable memory.
*/
MEM_RDONLY = BIT(1 + BPF_BASE_TYPE_BITS),
__BPF_TYPE_LAST_FLAG = MEM_RDONLY,