This is a note to let you know that I've just added the patch titled mm/mmap.c: do not blow on PROT_NONE MAP_FIXED holes in the stack to the 3.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: mm-mmap.c-do-not-blow-on-prot_none-map_fixed-holes-in-the-stack.patch and it can be found in the queue-3.18 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 561b5e0709e4a248c67d024d4d94b6e31e3edf2f Mon Sep 17 00:00:00 2001 From: Michal Hocko <mhocko@xxxxxxxx> Date: Mon, 10 Jul 2017 15:49:51 -0700 Subject: mm/mmap.c: do not blow on PROT_NONE MAP_FIXED holes in the stack From: Michal Hocko <mhocko@xxxxxxxx> commit 561b5e0709e4a248c67d024d4d94b6e31e3edf2f upstream. Commit 1be7107fbe18 ("mm: larger stack guard gap, between vmas") has introduced a regression in some rust and Java environments which are trying to implement their own stack guard page. They are punching a new MAP_FIXED mapping inside the existing stack Vma. This will confuse expand_{downwards,upwards} into thinking that the stack expansion would in fact get us too close to an existing non-stack vma which is a correct behavior wrt safety. It is a real regression on the other hand. Let's work around the problem by considering PROT_NONE mapping as a part of the stack. This is a gros hack but overflowing to such a mapping would trap anyway an we only can hope that usespace knows what it is doing and handle it propely. Fixes: 1be7107fbe18 ("mm: larger stack guard gap, between vmas") Link: http://lkml.kernel.org/r/20170705182849.GA18027@xxxxxxxxxxxxxx Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> Debugged-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: Ben Hutchings <ben@xxxxxxxxxxxxxxx> Cc: Willy Tarreau <w@xxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/mmap.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2191,7 +2191,8 @@ int expand_upwards(struct vm_area_struct gap_addr = TASK_SIZE; next = vma->vm_next; - if (next && next->vm_start < gap_addr) { + if (next && next->vm_start < gap_addr && + (next->vm_flags & (VM_WRITE|VM_READ|VM_EXEC))) { if (!(next->vm_flags & VM_GROWSUP)) return -ENOMEM; /* Check that both stack segments have the same anon_vma? */ @@ -2271,7 +2272,8 @@ int expand_downwards(struct vm_area_stru if (gap_addr > address) return -ENOMEM; prev = vma->vm_prev; - if (prev && prev->vm_end > gap_addr) { + if (prev && prev->vm_end > gap_addr && + (prev->vm_flags & (VM_WRITE|VM_READ|VM_EXEC))) { if (!(prev->vm_flags & VM_GROWSDOWN)) return -ENOMEM; /* Check that both stack segments have the same anon_vma? */ Patches currently in stable-queue which might be from mhocko@xxxxxxxx are queue-3.18/hwpoison-memcg-forcibly-uncharge-lru-pages.patch queue-3.18/mm-mmap.c-do-not-blow-on-prot_none-map_fixed-holes-in-the-stack.patch