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authorRoman Gushchin <klamm@yandex-team.ru>2015-02-11 15:28:42 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-03-18 13:31:23 +0100
commit040f4b16ef414f6cb8926af0c02008e88afc1db7 (patch)
tree31ef2f21a00705f0b3df81dfbc7f0a57b398d783 /mm
parent2ea6a268286566ddf365800ec2cbb458bedf55ab (diff)
downloadlwn-040f4b16ef414f6cb8926af0c02008e88afc1db7.tar.gz
lwn-040f4b16ef414f6cb8926af0c02008e88afc1db7.zip
mm/nommu.c: fix arithmetic overflow in __vm_enough_memory()
commit 8138a67a5557ffea3a21dfd6f037842d4e748513 upstream. I noticed that "allowed" can easily overflow by falling below 0, because (total_vm / 32) can be larger than "allowed". The problem occurs in OVERCOMMIT_NONE mode. In this case, a huge allocation can success and overcommit the system (despite OVERCOMMIT_NONE mode). All subsequent allocations will fall (system-wide), so system become unusable. The problem was masked out by commit c9b1d0981fcc ("mm: limit growth of 3% hardcoded other user reserve"), but it's easy to reproduce it on older kernels: 1) set overcommit_memory sysctl to 2 2) mmap() large file multiple times (with VM_SHARED flag) 3) try to malloc() large amount of memory It also can be reproduced on newer kernels, but miss-configured sysctl_user_reserve_kbytes is required. Fix this issue by switching to signed arithmetic here. Signed-off-by: Roman Gushchin <klamm@yandex-team.ru> Cc: Andrew Shewmaker <agshew@gmail.com> Cc: Rik van Riel <riel@redhat.com> Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/nommu.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/mm/nommu.c b/mm/nommu.c
index 3ee4f74fbfbe..76b3f90ada7b 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1905,7 +1905,7 @@ EXPORT_SYMBOL(unmap_mapping_range);
*/
int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
{
- unsigned long free, allowed, reserve;
+ long free, allowed, reserve;
vm_acct_memory(pages);
@@ -1969,7 +1969,7 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
*/
if (mm) {
reserve = sysctl_user_reserve_kbytes >> (PAGE_SHIFT - 10);
- allowed -= min(mm->total_vm / 32, reserve);
+ allowed -= min_t(long, mm->total_vm / 32, reserve);
}
if (percpu_counter_read_positive(&vm_committed_as) < allowed)