[PATCH] mm: Fix hiding the stack guard page in proc

[Stefan Bader]

Commit d7824370e26325c881b665350ce64fb0a4fde24a tried to hide the stack
guard page from user-space by adapting mlock and hiding it in /proc.
Commit 7798330ac8114c731cfab83e634c6ecedaa233d7 fixed the mlock part,
using the newly added double linked vma lists.
Still the proc change would hide the first page of each stack vma which
would be wrong for those vmas that are just continuations of the stack
after its vma has been split.

Signed-off-by: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxx
---
 fs/proc/task_mmu.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 439fc1f..2e302b4 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -224,7 +224,9 @@ static void show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
 	/* We don't show the stack guard page in /proc/maps */
 	start = vma->vm_start;
 	if (vma->vm_flags & VM_GROWSDOWN)
-		start += PAGE_SIZE;
+		if (!vma->vm_prev || vma->vm_prev->vm_flags != VM_GROWSDOWN ||
+		    vma->vm_start != vma->vm_prev->vm_end)
+			start += PAGE_SIZE;
 
 	seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu %n",
 			start,
-- 
1.7.0.4


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