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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: "Gustavo A. R. Silva" <gustavoars@kernel.org> Reviewed-by: Mimi Zohar <zohar@linux.ibm.com> Reviewed-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/ZSRaDcJNARUUWUwS@work Signed-off-by: Kees Cook <keescook@chromium.org>
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@ -29,7 +29,7 @@ struct modsig {
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* storing the signature.
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*/
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int raw_pkcs7_len;
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u8 raw_pkcs7[];
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u8 raw_pkcs7[] __counted_by(raw_pkcs7_len);
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};
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/*
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@ -65,10 +65,11 @@ int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
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buf_len -= sig_len + sizeof(*sig);
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/* Allocate sig_len additional bytes to hold the raw PKCS#7 data. */
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hdr = kzalloc(sizeof(*hdr) + sig_len, GFP_KERNEL);
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hdr = kzalloc(struct_size(hdr, raw_pkcs7, sig_len), GFP_KERNEL);
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if (!hdr)
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return -ENOMEM;
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hdr->raw_pkcs7_len = sig_len;
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hdr->pkcs7_msg = pkcs7_parse_message(buf + buf_len, sig_len);
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if (IS_ERR(hdr->pkcs7_msg)) {
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rc = PTR_ERR(hdr->pkcs7_msg);
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@ -77,7 +78,6 @@ int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
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}
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memcpy(hdr->raw_pkcs7, buf + buf_len, sig_len);
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hdr->raw_pkcs7_len = sig_len;
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/* We don't know the hash algorithm yet. */
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hdr->hash_algo = HASH_ALGO__LAST;
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