Commit 68a8f644 authored by Gustavo A. R. Silva's avatar Gustavo A. R. Silva Committed by Kees Cook
Browse files

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



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: default avatar"Gustavo A. R. Silva" <gustavoars@kernel.org>
Reviewed-by: default avatarMimi Zohar <zohar@linux.ibm.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/ZSRaDcJNARUUWUwS@work


Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent 8d7af820

security/integrity/ima/ima_modsig.c

+3 −3
Original line number Diff line number Diff line
@@ -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;