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Increased MBEDTLS_BEFORE_COLON (size of temporary buffer) to 32 #10433

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Increased MBEDTLS_BEFORE_COLON (size of temporary buffer) to 32 #10433

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3 changes: 2 additions & 1 deletion library/x509_crt.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1744,7 +1744,7 @@ static int x509_info_cert_policies(char **buf, size_t *size,
/*
* Return an informational string about the certificate.
*/
#define MBEDTLS_BEFORE_COLON 18
#define MBEDTLS_BEFORE_COLON 32
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Why 32? And why update only this and not the corresponding _STR macro below?

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@Mario-Klebsch Mario-Klebsch Oct 2, 2025 •
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Why 32?

Increasing the buffer size by 2 would have been sufficient. But I wanted to have some spara space, just in case someone changes mbedtls_x509_key_size_helper().

And why update only this and not the corresponding _STR macro below?

Changing the MBEDTLS_BEFORE_COLON enlarges the buffer and makes sure, that no MBEDTLS_ERR_X509_BUFFER_TOO_SMALL-error is generated.

Changing the MBEDTLS_BEFORE_COLON_STR macro changes the format string for printf in a way, that is does not match the other printf-statements. Here is a sample output:

cert. version     : 3
serial number     : F7:B9:58:6A:3B:C7:61:9A
issuer name       : CN=Intermediate CA
subject name      : CN=Server
issued  on        : 2025-10-02 08:48:33
expires on        : 2035-09-30 08:48:33
signed using      : ECDSA with SHA256
EC key size       : 256 bits
basic constraints : CA=false
key usage         : Digital Signature

When the MBEDTLS_BEFORE_COLON_STR-Macro is changed, the other printf format strings would need to be updated too.

I choose to not update the MBEDTLS_BEFORE_COLON_STR-Macro, because IMHO that is not a problem. In cases, when no MBEDTLS_ERR_X509_BUFFER_TOO_SMALL error is generated, the output of mbedtls_x509_crt_info() would be the same as before.

In case the current implementation fails with MBEDTLS_ERR_X509_BUFFER_TOO_SMALL, the colon in the info string would not be adjusted to the colons of the other lines.

To me, this seems like a reasonable compromize.

#define MBEDTLS_BEFORE_COLON_STR "18"
int mbedtls_x509_crt_info(char *buf, size_t size, const char *prefix,
const mbedtls_x509_crt *crt)
Expand Down Expand Up @@ -1807,6 +1807,7 @@ int mbedtls_x509_crt_info(char *buf, size_t size, const char *prefix,
/* Key size */
if ((ret = mbedtls_x509_key_size_helper(key_size_str, MBEDTLS_BEFORE_COLON,
mbedtls_pk_get_name(&crt->pk))) != 0) {
assert(ret != MBEDTLS_ERR_X509_BUFFER_TOO_SMALL);
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We don't use assert in the library.

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@Mario-Klebsch Mario-Klebsch Oct 2, 2025 •
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The purpose of assert()ions is to signal errors in the internal logic of some software. In this case, supplying an insuffently sized buffer to mbedtls_x509_key_size_helper() in an error in the program logic. This is the reason, why I added an assertion.

Just remove it from my contribution, if you don't want to use this extra instrumentation in your code.

return ret;
}

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3 changes: 2 additions & 1 deletion library/x509_csr.c
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Original file line number Diff line number Diff line change
Expand Up @@ -519,7 +519,7 @@ int mbedtls_x509_csr_parse_file(mbedtls_x509_csr *csr, const char *path)
#endif /* MBEDTLS_FS_IO */

#if !defined(MBEDTLS_X509_REMOVE_INFO)
#define MBEDTLS_BEFORE_COLON 14
#define MBEDTLS_BEFORE_COLON 32
#define MBEDTLS_BEFORE_COLON_STR "14"
/*
* Return an informational string about the CSR.
Expand Down Expand Up @@ -552,6 +552,7 @@ int mbedtls_x509_csr_info(char *buf, size_t size, const char *prefix,

if ((ret = mbedtls_x509_key_size_helper(key_size_str, MBEDTLS_BEFORE_COLON,
mbedtls_pk_get_name(&csr->pk))) != 0) {
assert(ret != MBEDTLS_ERR_X509_BUFFER_TOO_SMALL);
return ret;
}

Expand Down