[PATCH 09/10] meson: wire up unsafe SHA1 backend

[Patrick Steinhardt <ps@xxxxxx>]

In 06c92dafb8 (Makefile: allow specifying a SHA-1 for non-cryptographic
uses, 2024-09-26), we have introduced a cryptographically-insecure
backend for SHA1 that can optionally be used in some contexts where the
processed data is not security relevant. This effort was in-flight with
the effort to introduce Meson, so we don't have an equivalent here.

Wire up a new build option that lets users pick an unsafe SHA1 backend.

Note that for simplicity's sake we have to drop the error condition
around an unhandled SHA1 backend. This should be fine though given that
Meson verifies the value for combo-options for us.

Signed-off-by: Patrick Steinhardt <ps@xxxxxx>
---
 meson.build       | 40 ++++++++++++++++++++++++++++++----------
 meson_options.txt |  2 ++
 2 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/meson.build b/meson.build
index 46f807899b7bae33dd6aa7a94a54931d69ab0d62..dc82c23cb4f07646a9a7bb96fefcf832f9840975 100644
--- a/meson.build
+++ b/meson.build
@@ -1327,15 +1327,16 @@ endif
 
 https_backend = get_option('https_backend')
 sha1_backend = get_option('sha1_backend')
+sha1_unsafe_backend = get_option('sha1_unsafe_backend')
 sha256_backend = get_option('sha256_backend')
 
-security_framework = dependency('Security', required: 'CommonCrypto' in [https_backend, sha1_backend])
+security_framework = dependency('Security', required: 'CommonCrypto' in [https_backend, sha1_backend, sha1_unsafe_backend])
 core_foundation_framework = dependency('CoreFoundation', required: security_framework.found())
 if https_backend == 'auto' and security_framework.found()
   https_backend = 'CommonCrypto'
 endif
 
-openssl_required = 'openssl' in [https_backend, sha1_backend, sha256_backend]
+openssl_required = 'openssl' in [https_backend, sha1_backend, sha1_unsafe_backend, sha256_backend]
 openssl = dependency('openssl', required: openssl_required, default_options: ['default_library=static'])
 if https_backend == 'auto' and openssl.found()
   https_backend = 'openssl'
@@ -1368,19 +1369,38 @@ if sha1_backend == 'sha1dc'
     'sha1dc/sha1.c',
     'sha1dc/ubc_check.c',
   ]
-elif sha1_backend == 'CommonCrypto'
+endif
+if sha1_backend == 'CommonCrypto' or sha1_unsafe_backend == 'CommonCrypto'
+  if sha1_backend == 'CommonCrypto'
+    libgit_c_args += '-DSHA1_APPLE'
+  endif
+  if sha1_unsafe_backend == 'CommonCrypto'
+    libgit_c_args += '-DSHA1_APPLE_UNSAFE'
+  endif
+
   libgit_c_args += '-DCOMMON_DIGEST_FOR_OPENSSL'
-  libgit_c_args += '-DSHA1_APPLE'
   # Apple CommonCrypto requires chunking
   libgit_c_args += '-DSHA1_MAX_BLOCK_SIZE=1024L*1024L*1024L'
-elif sha1_backend == 'openssl'
-  libgit_c_args += '-DSHA1_OPENSSL'
+endif
+if sha1_backend == 'openssl' or sha1_unsafe_backend == 'openssl'
+  if sha1_backend == 'openssl'
+    libgit_c_args += '-DSHA1_OPENSSL'
+  endif
+  if sha1_unsafe_backend == 'openssl'
+    libgit_c_args += '-DSHA1_OPENSSL_UNSAFE'
+  endif
+
   libgit_dependencies += openssl
-elif sha1_backend == 'block'
-  libgit_c_args += '-DSHA1_BLK'
+endif
+if sha1_backend == 'block' or sha1_unsafe_backend == 'block'
+  if sha1_backend == 'block'
+    libgit_c_args += '-DSHA1_BLK'
+  endif
+  if sha1_unsafe_backend == 'block'
+    libgit_c_args += '-DSHA1_BLK_UNSAFE'
+  endif
+
   libgit_sources += 'block-sha1/sha1.c'
-else
-  error('Unhandled SHA1 backend ' + sha1_backend)
 endif
 
 if sha256_backend == 'openssl'
diff --git a/meson_options.txt b/meson_options.txt
index d8d283982bcdd0f688556e0102c0133061dfb304..8282b1dea8e852fbd3a28309a96fdc83412f245d 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -51,6 +51,8 @@ option('https_backend', type: 'combo', value: 'auto', choices: ['auto', 'openssl
   description: 'The HTTPS backend to use when connecting to remotes.')
 option('sha1_backend', type: 'combo', choices: ['openssl', 'block', 'sha1dc', 'CommonCrypto'], value: 'sha1dc',
   description: 'The backend used for hashing objects with the SHA1 object format.')
+option('sha1_unsafe_backend', type: 'combo', choices: ['openssl', 'block', 'CommonCrypto', 'none'], value: 'none',
+  description: 'The backend used for hashing data with the SHA1 object format in case no cryptographic security is needed.')
 option('sha256_backend', type: 'combo', choices: ['openssl', 'nettle', 'gcrypt', 'block'], value: 'block',
   description: 'The backend used for hashing objects with the SHA256 object format.')
 

-- 
2.48.0.rc0.311.gb6c66824c1.dirty