Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).
Also, relocate `hdr->raw_pkcs7_len = sig_len;` so that the __counted_by
annotation has effect, and flex-array member `raw_pkcs7` can be properly
bounds-checked at run-time.
While there, use struct_size() helper, instead of the open-coded
version, to calculate the size for the allocation of the whole
flexible structure, including of course, the flexible-array member.
This code was found with the help of Coccinelle, and audited and
fixed manually.
Signed-off-by: Gustavo A. R. Silva <[email protected]>
---
security/integrity/ima/ima_modsig.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/security/integrity/ima/ima_modsig.c b/security/integrity/ima/ima_modsig.c
index 3e7bee30080f..3265d744d5ce 100644
--- a/security/integrity/ima/ima_modsig.c
+++ b/security/integrity/ima/ima_modsig.c
@@ -29,7 +29,7 @@ struct modsig {
* storing the signature.
*/
int raw_pkcs7_len;
- u8 raw_pkcs7[];
+ u8 raw_pkcs7[] __counted_by(raw_pkcs7_len);
};
/*
@@ -65,10 +65,11 @@ int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
buf_len -= sig_len + sizeof(*sig);
/* Allocate sig_len additional bytes to hold the raw PKCS#7 data. */
- hdr = kzalloc(sizeof(*hdr) + sig_len, GFP_KERNEL);
+ hdr = kzalloc(struct_size(hdr, raw_pkcs7, sig_len), GFP_KERNEL);
if (!hdr)
return -ENOMEM;
+ hdr->raw_pkcs7_len = sig_len;
hdr->pkcs7_msg = pkcs7_parse_message(buf + buf_len, sig_len);
if (IS_ERR(hdr->pkcs7_msg)) {
rc = PTR_ERR(hdr->pkcs7_msg);
@@ -77,7 +78,6 @@ int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
}
memcpy(hdr->raw_pkcs7, buf + buf_len, sig_len);
- hdr->raw_pkcs7_len = sig_len;
/* We don't know the hash algorithm yet. */
hdr->hash_algo = HASH_ALGO__LAST;
--
2.34.1
On Mon, Oct 09, 2023 at 01:52:45PM -0600, Gustavo A. R. Silva wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
> array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
>
> Also, relocate `hdr->raw_pkcs7_len = sig_len;` so that the __counted_by
> annotation has effect, and flex-array member `raw_pkcs7` can be properly
> bounds-checked at run-time.
>
> While there, use struct_size() helper, instead of the open-coded
> version, to calculate the size for the allocation of the whole
> flexible structure, including of course, the flexible-array member.
>
> This code was found with the help of Coccinelle, and audited and
> fixed manually.
>
> Signed-off-by: Gustavo A. R. Silva <[email protected]>
Looks right; good catch on moving the assignment.
Reviewed-by: Kees Cook <[email protected]>
--
Kees Cook
On Mon, 2023-10-09 at 13:52 -0600, Gustavo A. R. Silva wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
> array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
>
> Also, relocate `hdr->raw_pkcs7_len = sig_len;` so that the __counted_by
> annotation has effect, and flex-array member `raw_pkcs7` can be properly
> bounds-checked at run-time.
>
> While there, use struct_size() helper, instead of the open-coded
> version, to calculate the size for the allocation of the whole
> flexible structure, including of course, the flexible-array member.
>
> This code was found with the help of Coccinelle, and audited and
> fixed manually.
>
> Signed-off-by: Gustavo A. R. Silva <[email protected]>
Reviewed-by: Mimi Zohar <[email protected]>
On Mon, 09 Oct 2023 13:52:45 -0600, Gustavo A. R. Silva wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
> array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
>
> Also, relocate `hdr->raw_pkcs7_len = sig_len;` so that the __counted_by
> annotation has effect, and flex-array member `raw_pkcs7` can be properly
> bounds-checked at run-time.
>
> [...]
Applied to for-next/hardening, thanks!
[1/1] ima: Add __counted_by for struct modsig and use struct_size()
https://git.kernel.org/kees/c/68a8f644575b
Take care,
--
Kees Cook