diff mbox series

ima: Add __counted_by for struct modsig and use struct_size()

Message ID ZSRaDcJNARUUWUwS@work
State New
Headers
Series ima: Add __counted_by for struct modsig and use struct_size() |

Commit Message

Gustavo A. R. Silva Oct. 9, 2023, 7:52 p.m. UTC 
  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 <gustavoars@kernel.org>
---
 security/integrity/ima/ima_modsig.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

Kees Cook Oct. 9, 2023, 7:55 p.m. UTC | #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 <gustavoars@kernel.org>

Looks right; good catch on moving the assignment.

Reviewed-by: Kees Cook <keescook@chromium.org>
Mimi Zohar Oct. 18, 2023, 6:16 p.m. UTC | #2 
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 <gustavoars@kernel.org>

Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Kees Cook Oct. 24, 2023, 9:18 p.m. UTC | #3 
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,
diff mbox series

Patch

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;