From 08751e477f0eacf90a72df15dbda94f95c794fda Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Tue, 30 Oct 2018 15:05:14 -0700 Subject: [PATCH] lib/bitmap.c: fix remaining space computation in bitmap_print_to_pagebuf [ Upstream commit ce1091d471107dbf6f91db66a480a25950c9b9ff ] For various alignments of buf, the current expression computes 4096 ok 4095 ok 8190 8189 ... 4097 i.e., if the caller has already written two bytes into the page buffer, len is 8190 rather than 4094, because PTR_ALIGN aligns up to the next boundary. So if the printed version of the bitmap is huge, scnprintf() ends up writing beyond the page boundary. I don't think any current callers actually write anything before bitmap_print_to_pagebuf, but the API seems to be designed to allow it. [akpm@linux-foundation.org: use offset_in_page(), per Andy] [akpm@linux-foundation.org: include mm.h for offset_in_page()] Link: http://lkml.kernel.org/r/20180818131623.8755-7-linux@rasmusvillemoes.dk Signed-off-by: Rasmus Villemoes Reviewed-by: Andy Shevchenko Cc: Yury Norov Cc: Rasmus Villemoes Cc: Sudeep Holla Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- lib/bitmap.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/lib/bitmap.c b/lib/bitmap.c index 2fd07f6df0b8..c4ca9ceb09fe 100644 --- a/lib/bitmap.c +++ b/lib/bitmap.c @@ -13,6 +13,7 @@ #include #include #include +#include #include #include #include @@ -466,14 +467,15 @@ EXPORT_SYMBOL(bitmap_parse_user); * ranges if list is specified or hex digits grouped into comma-separated * sets of 8 digits/set. Returns the number of characters written to buf. * - * It is assumed that @buf is a pointer into a PAGE_SIZE area and that - * sufficient storage remains at @buf to accommodate the - * bitmap_print_to_pagebuf() output. + * It is assumed that @buf is a pointer into a PAGE_SIZE, page-aligned + * area and that sufficient storage remains at @buf to accommodate the + * bitmap_print_to_pagebuf() output. Returns the number of characters + * actually printed to @buf, excluding terminating '\0'. */ int bitmap_print_to_pagebuf(bool list, char *buf, const unsigned long *maskp, int nmaskbits) { - ptrdiff_t len = PTR_ALIGN(buf + PAGE_SIZE - 1, PAGE_SIZE) - buf; + ptrdiff_t len = PAGE_SIZE - offset_in_page(buf); int n = 0; if (len > 1)