[PATCH] dir.c: skip .gitignore, etc larger than INT_MAX

From: Jeff King <peff@peff.net>
Date: May 31, 2024, 12:00 UTC
Message-ID: <20240531120034.GA442032@coredump.intra.peff.net>

We use add_patterns() to read .gitignore, .git/info/exclude, etc, as well as other pattern-like files like sparse-checkout. The parser for these uses an "int" as an index, meaning that files over 2GB will generally cause signed integer overflow and out-of-bounds access.

This is unlikely to happen in any real files, but we do read .gitignore files from the tree. A malicious tree could cause an out-of-bounds read and segfault (we also write NULs over newlines, so in theory it could be an out-of-bounds write, too, but as we go char-by-char, the first thing that happens is trying to read a negative 2GB offset).

We could fix the most obvious issue by replacing one "int" with a "size_t". But there are tons of "int" sprinkled throughout this code for things like pattern lengths, number of patterns, and so on. Since nobody would actually want a 2GB .gitignore file, an easy defensive measure is to just refuse to parse them.

The "int" in question is in add_patterns_from_buffer(), so we could catch it there. But by putting the checks in its two callers, we can produce more useful error messages.

Signed-off-by: Jeff King <peff@peff.net>
---
Just something I noticed while working on leaks nearby.

 dir.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/dir.c b/dir.c
index f6066cc01d..914060edfd 100644
--- a/dir.c
+++ b/dir.c
@@ -30,6 +30,7 @@
 #include "symlinks.h"
 #include "trace2.h"
 #include "tree.h"
+#include "hex.h"
 
 /*
  * Tells read_directory_recursive how a file or directory should be treated.
@@ -1148,6 +1149,12 @@ static int add_patterns(const char *fname, const char *base, int baselen,
 		}
 	}
 
+	if (size > INT_MAX) {
+		warning("ignoring excessively large pattern file: %s", fname);
+		free(buf);
+		return -1;
+	}
+
 	add_patterns_from_buffer(buf, size, base, baselen, pl);
 	return 0;
 }
@@ -1204,6 +1211,13 @@ int add_patterns_from_blob_to_list(
 	if (r != 1)
 		return r;
 
+	if (size > INT_MAX) {
+		warning("ignoring excessively large pattern blob: %s",
+			oid_to_hex(oid));
+		free(buf);
+		return -1;
+	}
+
 	add_patterns_from_buffer(buf, size, base, baselen, pl);
 	return 0;
 }

-- 
2.45.1.727.ge984192922