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bpf: Lift hashtab key_size limit

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Currently key_size of hashtab is limited to MAX_BPF_STACK.
As the key of hashtab can also be a value from a per cpu map it can be
larger than MAX_BPF_STACK.

The use-case for this patch originates to implement allow/disallow
lists for files and file paths. The maximum length of file paths is
defined by PATH_MAX with 4096 chars including nul.
This limit exceeds MAX_BPF_STACK.

Changelog:

v5:
 - Fix cast overflow

v4:
 - Utilize BPF skeleton in tests
 - Rebase

v3:
 - Rebase

v2:
 - Add a test for bpf side

Signed-off-by: Florian Lehner <dev@der-flo.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20201029201442.596690-1-dev@der-flo.net
This commit is contained in:
Florian Lehner
2020-10-29 21:14:42 +01:00
committed by Alexei Starovoitov
parent b6b466a81f
commit c6bde958a6
4 changed files with 94 additions and 12 deletions
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16
kernel/bpf/hashtab.c
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@@ -415,17 +415,11 @@ static int htab_map_alloc_check(union bpf_attr *attr)
attr->value_size == 0)
return -EINVAL;
if (attr->key_size > MAX_BPF_STACK)
/* eBPF programs initialize keys on stack, so they cannot be
* larger than max stack size
*/
return -E2BIG;
if (attr->value_size >= KMALLOC_MAX_SIZE -
MAX_BPF_STACK - sizeof(struct htab_elem))
/* if value_size is bigger, the user space won't be able to
* access the elements via bpf syscall. This check also makes
* sure that the elem_size doesn't overflow and it's
if ((u64)attr->key_size + attr->value_size >= KMALLOC_MAX_SIZE -
sizeof(struct htab_elem))
/* if key_size + value_size is bigger, the user space won't be
* able to access the elements via bpf syscall. This check
* also makes sure that the elem_size doesn't overflow and it's
* kmalloc-able later in htab_map_update_elem()
*/
return -E2BIG;