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authorHugh Dickins <hugh.dickins@tiscali.co.uk>2010-03-05 13:42:12 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2010-03-06 11:26:26 -0800
commitad2bd7e0e9647cd48593a6b3a2be07dc2c2d28ed (patch)
tree247c1c46e4c6948d482878f1c85c99cf180ff024 /mm
parentfc148a5f7e0532750c312385c7ee9fa3e9311f34 (diff)
downloadconfigs-ad2bd7e0e9647cd48593a6b3a2be07dc2c2d28ed.tar.gz
mm/swapfile.c: fix swapon size off-by-one
There's an off-by-one disagreement between mkswap and swapon about the meaning of swap_header last_page: mkswap (in all versions I've looked at: util-linux-ng and BusyBox and old util-linux; probably as far back as 1999) consistently means the offset (in page units) of the last page of the swap area, whereas kernel sys_swapon (as far back as 2.2 and 2.3) strangely takes it to mean the size (in page units) of the swap area. This disagreement is the safe way round; but it's worrying people, and loses us one page of swap. The fix is not just to add one to nr_good_pages: we need to get maxpages (the size of the swap_map array) right before that; and though that is an unsigned long, be careful not to overflow the unsigned int p->max which later holds it (probably why header uses __u32 last_page instead of size). Why did we subtract one from the maximum swp_offset to calculate maxpages? Though it was probably me who made that change in 2.4.10, I don't get it: and now we should be adding one (without risk of overflow in this case). Fix the handling of swap_header badpages: it could have overrun the swap_map when very large swap area used on a more limited architecture. Remove pre-initializations of swap_header, nr_good_pages and maxpages: those date from when sys_swapon was supporting other versions of header. Reported-by: Nitin Gupta <ngupta@vflare.org> Reported-by: Jarkko Lavinen <jarkko.lavinen@nokia.com> Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/swapfile.c31
1 files changed, 18 insertions, 13 deletions
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 187a21f8b7b..4a986127f15 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1760,11 +1760,11 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
unsigned int type;
int i, prev;
int error;
- union swap_header *swap_header = NULL;
- unsigned int nr_good_pages = 0;
+ union swap_header *swap_header;
+ unsigned int nr_good_pages;
int nr_extents = 0;
sector_t span;
- unsigned long maxpages = 1;
+ unsigned long maxpages;
unsigned long swapfilepages;
unsigned char *swap_map = NULL;
struct page *page = NULL;
@@ -1923,9 +1923,13 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
* swap pte.
*/
maxpages = swp_offset(pte_to_swp_entry(
- swp_entry_to_pte(swp_entry(0, ~0UL)))) - 1;
- if (maxpages > swap_header->info.last_page)
- maxpages = swap_header->info.last_page;
+ swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
+ if (maxpages > swap_header->info.last_page) {
+ maxpages = swap_header->info.last_page + 1;
+ /* p->max is an unsigned int: don't overflow it */
+ if ((unsigned int)maxpages == 0)
+ maxpages = UINT_MAX;
+ }
p->highest_bit = maxpages - 1;
error = -EINVAL;
@@ -1949,23 +1953,24 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
}
memset(swap_map, 0, maxpages);
+ nr_good_pages = maxpages - 1; /* omit header page */
+
for (i = 0; i < swap_header->info.nr_badpages; i++) {
- int page_nr = swap_header->info.badpages[i];
- if (page_nr <= 0 || page_nr >= swap_header->info.last_page) {
+ unsigned int page_nr = swap_header->info.badpages[i];
+ if (page_nr == 0 || page_nr > swap_header->info.last_page) {
error = -EINVAL;
goto bad_swap;
}
- swap_map[page_nr] = SWAP_MAP_BAD;
+ if (page_nr < maxpages) {
+ swap_map[page_nr] = SWAP_MAP_BAD;
+ nr_good_pages--;
+ }
}
error = swap_cgroup_swapon(type, maxpages);
if (error)
goto bad_swap;
- nr_good_pages = swap_header->info.last_page -
- swap_header->info.nr_badpages -
- 1 /* header page */;
-
if (nr_good_pages) {
swap_map[0] = SWAP_MAP_BAD;
p->max = maxpages;