4.9-stable review patch. If anyone has any objections, please let me know.
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From: Tom Abraham tabraham@suse.com
[ Upstream commit a06ad633a37c64a0cd4c229fc605cee8725d376e ]
Calling swapon() on a zero length swap file on SSD can lead to a divide-by-zero.
Although creating such files isn't possible with mkswap and they woud be considered invalid, it would be better for the swapon code to be more robust and handle this condition gracefully (return -EINVAL). Especially since the fix is small and straightforward.
To help with wear leveling on SSD, the swapon syscall calculates a random position in the swap file using modulo p->highest_bit, which is set to maxpages - 1 in read_swap_header.
If the swap file is zero length, read_swap_header sets maxpages=1 and last_page=0, resulting in p->highest_bit=0 and we divide-by-zero when we modulo p->highest_bit in swapon syscall.
This can be prevented by having read_swap_header return zero if last_page is zero.
Link: http://lkml.kernel.org/r/5AC747C1020000A7001FA82C@prv-mh.provo.novell.com Signed-off-by: Thomas Abraham tabraham@suse.com Reported-by: Mark.Landis@Teradata.com Reviewed-by: Andrew Morton akpm@linux-foundation.org Cc: Randy Dunlap rdunlap@infradead.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/swapfile.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -2271,6 +2271,10 @@ static unsigned long read_swap_header(st maxpages = swp_offset(pte_to_swp_entry( swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1; last_page = swap_header->info.last_page; + if (!last_page) { + pr_warn("Empty swap-file\n"); + return 0; + } if (last_page > maxpages) { pr_warn("Truncating oversized swap area, only using %luk out of %luk\n", maxpages << (PAGE_SHIFT - 10),