git name-rev writes beyond the end of malloc() with large generations
When using git name-rev on my kernel tree I triggered a malloc()
corruption warning from glibc.
apw@pinky$ git log --pretty=one $N/base.. | git name-rev --stdin
*** glibc detected *** malloc(): memory corruption: 0x0bff8950 ***
Aborted
This comes from name_rev() which is building the name of the revision
in a malloc'd string, which it sprintf's into:
char *new_name = xmalloc(len + 8);
[...]
sprintf(new_name, "%.*s~%d^%d", len, tip_name,
generation, parent_number);
This allocation is only sufficient if the generation number is
less than 5 digits, in my case generation was 13432. In reality
parent_number can be up to 16 so that also can require two digits,
reducing us to 3 digits before we are at risk of blowing this
allocation.
This patch introduces a decimal_length() which approximates the
number of digits a type may hold, it produces the following:
Type Longest Value Len Est
---- ------------- --- ---
unsigned char 256 3 4
unsigned short 65536 5 6
unsigned long 4294967296 10 11
unsigned long long 18446744073709551616 20 21
char -128 4 4
short -32768 6 6
long -2147483648 11 11
long long -9223372036854775808 20 21
This is then used to size the new_name.
Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/git-compat-util.h b/git-compat-util.h
index bd93b62..7ed8b88 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -13,6 +13,9 @@
#define ARRAY_SIZE(x) (sizeof(x)/sizeof(x[0]))
+/* Approximation of the length of the decimal representation of this type. */
+#define decimal_length(x) ((int)(sizeof(x) * 2.56 + 0.5) + 1)
+
#if !defined(__APPLE__) && !defined(__FreeBSD__)
#define _XOPEN_SOURCE 600 /* glibc2 and AIX 5.3L need 500, OpenBSD needs 600 for S_ISLNK() */
#define _XOPEN_SOURCE_EXTENDED 1 /* AIX 5.3L needs this */
