Match against local system libc first in libcdb

CHANGELOG.md

@@ -85,6 +85,7 @@ The table below shows which release corresponds to each branch, and what date th
 - [#2189][2189] Explicitly define p64/u64 functions for IDE support
 - [#2339][2339] Fix: Allow setting attributes on gdb Breakpoints
 - [#2323][2323] Retry failed lookups after one week in libcdb
+- [#2325][2325] Match against local system libc first in libcdb
 
 [2242]: https://github.com/Gallopsled/pwntools/pull/2242
 [2277]: https://github.com/Gallopsled/pwntools/pull/2277
@@ -101,6 +102,7 @@ The table below shows which release corresponds to each branch, and what date th
 [2189]: https://github.com/Gallopsled/pwntools/pull/2189
 [2339]: https://github.com/Gallopsled/pwntools/pull/2339
 [2323]: https://github.com/Gallopsled/pwntools/pull/2323
+[2325]: https://github.com/Gallopsled/pwntools/pull/2325
 
 ## 4.12.0 (`beta`)
 

pwnlib/libcdb.py

@@ -14,14 +14,20 @@
 from pwnlib.log import getLogger
 from pwnlib.tubes.process import process
 from pwnlib.util.fiddling import enhex
+from pwnlib.util.hashes import sha1filehex, sha256filehex, md5filehex
 from pwnlib.util.misc import read
 from pwnlib.util.misc import which
 from pwnlib.util.misc import write
 from pwnlib.util.web import wget
 
 log = getLogger(__name__)
 
-HASHES = ['build_id', 'sha1', 'sha256', 'md5']
+HASHES = {
+    'build_id': lambda path: enhex(ELF(path, checksec=False).buildid or b''),
+    'sha1': sha1filehex,
+    'sha256': sha256filehex,
+    'md5': md5filehex,
+}
 DEBUGINFOD_SERVERS = [
     'https://debuginfod.elfutils.org/',
 ]
@@ -104,7 +110,23 @@ def provider_libc_rip(hex_encoded_id, hash_type):
         return None
     return data
 
-PROVIDERS = [provider_libcdb, provider_libc_rip]
+# Check if the local system libc matches the requested hash.
+def provider_local_system(hex_encoded_id, hash_type):
+    if hash_type == 'id':
+        return None
+    shell_path = os.environ.get('SHELL', None) or '/bin/sh'
+    if not os.path.exists(shell_path):
+        log.debug('Shell path %r does not exist. Skipping local system libc matching.', shell_path)
+        return None
+    local_libc = ELF(shell_path, checksec=False).libc
+    if not local_libc:
+        log.debug('Cannot lookup libc from shell %r. Skipping local system libc matching.', shell_path)
+        return None
+    if HASHES[hash_type](local_libc.path) == hex_encoded_id:
+        return local_libc.data
+    return None
+
+PROVIDERS = [provider_local_system, provider_libcdb, provider_libc_rip]
 
 def search_by_hash(hex_encoded_id, hash_type='build_id', unstrip=True):
     assert hash_type in HASHES, hash_type