path: root/mm
diff options
authorLinus Torvalds <torvalds@linux-foundation.org>2013-02-27 08:36:04 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2013-02-27 08:36:04 -0800
commit09884964335e85e897876d17783c2ad33cf8a2e0 (patch)
tree4cf0ea71bb20c8d81147614e90e53df3368405e5 /mm
parentd895cb1af15c04c522a25c79cc429076987c089b (diff)
mm: do not grow the stack vma just because of an overrun on preceding vma
The stack vma is designed to grow automatically (marked with VM_GROWSUP or VM_GROWSDOWN depending on architecture) when an access is made beyond the existing boundary. However, particularly if you have not limited your stack at all ("ulimit -s unlimited"), this can cause the stack to grow even if the access was really just one past *another* segment. And that's wrong, especially since we first grow the segment, but then immediately later enforce the stack guard page on the last page of the segment. So _despite_ first growing the stack segment as a result of the access, the kernel will then make the access cause a SIGSEGV anyway! So do the same logic as the guard page check does, and consider an access to within one page of the next segment to be a bad access, rather than growing the stack to abut the next segment. Reported-and-tested-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
1 files changed, 27 insertions, 0 deletions
diff --git a/mm/mmap.c b/mm/mmap.c
index 37a1fcac029..2664a47cec9 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2185,9 +2185,28 @@ int expand_downwards(struct vm_area_struct *vma,
return error;
+ * Note how expand_stack() refuses to expand the stack all the way to
+ * abut the next virtual mapping, *unless* that mapping itself is also
+ * a stack mapping. We want to leave room for a guard page, after all
+ * (the guard page itself is not added here, that is done by the
+ * actual page faulting logic)
+ *
+ * This matches the behavior of the guard page logic (see mm/memory.c:
+ * check_stack_guard_page()), which only allows the guard page to be
+ * removed under these circumstances.
+ */
int expand_stack(struct vm_area_struct *vma, unsigned long address)
+ struct vm_area_struct *next;
+ address &= PAGE_MASK;
+ next = vma->vm_next;
+ if (next && next->vm_start == address + PAGE_SIZE) {
+ if (!(next->vm_flags & VM_GROWSUP))
+ return -ENOMEM;
+ }
return expand_upwards(vma, address);
@@ -2209,6 +2228,14 @@ find_extend_vma(struct mm_struct *mm, unsigned long addr)
int expand_stack(struct vm_area_struct *vma, unsigned long address)
+ struct vm_area_struct *prev;
+ address &= PAGE_MASK;
+ prev = vma->vm_prev;
+ if (prev && prev->vm_end == address) {
+ if (!(prev->vm_flags & VM_GROWSDOWN))
+ return -ENOMEM;
+ }
return expand_downwards(vma, address);