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Subject[PATCH] security: integrity: Replace zero-length array with flexible-array member
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
int stuff;
struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
security/integrity/ima/ima.h | 2 +-
security/integrity/integrity.h | 4 ++--
2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 64317d95363e..da4246ee7e35 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -95,7 +95,7 @@ struct ima_template_entry {
u8 digest[TPM_DIGEST_SIZE]; /* sha1 or md5 measurement hash */
struct ima_template_desc *template_desc; /* template descriptor */
u32 template_data_len;
- struct ima_field_data template_data[0]; /* template related data */
+ struct ima_field_data template_data[]; /* template related data */
};

struct ima_queue_entry {
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index 543d277c7e48..3c7e8b902256 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -103,7 +103,7 @@ struct ima_digest_data {
} ng;
u8 data[2];
} xattr;
- u8 digest[0];
+ u8 digest[];
} __packed;

/*
@@ -115,7 +115,7 @@ struct signature_v2_hdr {
uint8_t hash_algo; /* Digest algorithm [enum hash_algo] */
__be32 keyid; /* IMA key identifier - not X509/PGP specific */
__be16 sig_size; /* signature size */
- uint8_t sig[0]; /* signature payload */
+ uint8_t sig[]; /* signature payload */
} __packed;

/* integrity data associated with an inode */
--
2.25.0
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