From d306f3d3513c62342fec4e31457766f2473f9e9a Mon Sep 17 00:00:00 2001 From: Jeff King Date: Thu, 5 Feb 2015 03:14:19 -0500 Subject: [PATCH] decimal_width: avoid integer overflow The decimal_width function originally appeared in blame.c as "lineno_width", and was designed for calculating the print-width of small-ish integer values (line numbers in text files). In ec7ff5b, it was made into a reusable function, and in dc801e7, we started using it to align diffstats. Binary files in a diffstat show byte counts rather than line numbers, meaning they can be quite large (e.g., consider adding or removing a 2GB file). decimal_width is not up to the challenge for two reasons: 1. It takes the value as an "int", whereas large files may easily surpass this. The value may be truncated, in which case we will produce an incorrect value. 2. It counts "up" by repeatedly multiplying another integer by 10 until it surpasses the value. This can cause an infinite loop when the value is close to the largest representable integer. For example, consider using a 32-bit signed integer, and a value of 2,140,000,000 (just shy of 2^31-1). We will count up and eventually see that 1,000,000,000 is smaller than our value. The next step would be to multiply by 10 and see that 10,000,000,000 is too large, ending the loop. But we can't represent that value, and we have signed overflow. This is technically undefined behavior, but a common behavior is to lose the high bits, in which case our iterator will certainly be less than the number. So we'll keep multiplying, overflow again, and so on. This patch changes the argument to a uintmax_t (the same type we use to store the diffstat information for binary filese), and counts "down" by repeatedly dividing our value by 10. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- cache.h | 2 +- pager.c | 8 ++++---- 2 files changed, 5 insertions(+), 5 deletions(-) diff --git a/cache.h b/cache.h index 29ed24b802..db02a2de7f 100644 --- a/cache.h +++ b/cache.h @@ -1213,7 +1213,7 @@ extern const char *pager_program; extern int pager_in_use(void); extern int pager_use_color; extern int term_columns(void); -extern int decimal_width(int); +extern int decimal_width(uintmax_t); extern int check_pager_config(const char *cmd); extern const char *editor_program; diff --git a/pager.c b/pager.c index fa19765eb9..314210351b 100644 --- a/pager.c +++ b/pager.c @@ -139,12 +139,12 @@ int term_columns(void) /* * How many columns do we need to show this number in decimal? */ -int decimal_width(int number) +int decimal_width(uintmax_t number) { - int i, width; + int width; - for (width = 1, i = 10; i <= number; width++) - i *= 10; + for (width = 1; number >= 10; width++) + number /= 10; return width; }