[SRU][Artful][PATCH 1/1] mm/madvise.c: fix madvise() infinite loop under special circumstances

[Kleber Sacilotto de Souza]

From: chenjie <chenjie6 at huawei.com>

CVE-2017-18208

MADVISE_WILLNEED has always been a noop for DAX (formerly XIP) mappings.
Unfortunately madvise_willneed() doesn't communicate this information
properly to the generic madvise syscall implementation.  The calling
convention is quite subtle there.  madvise_vma() is supposed to either
return an error or update &prev otherwise the main loop will never
advance to the next vma and it will keep looping for ever without a way
to get out of the kernel.

It seems this has been broken since introduction.  Nobody has noticed
because nobody seems to be using MADVISE_WILLNEED on these DAX mappings.

[mhocko at suse.com: rewrite changelog]
Link: http://lkml.kernel.org/r/20171127115318.911-1-guoxuenan@huawei.com
Fixes: fe77ba6f4f97 ("[PATCH] xip: madvice/fadvice: execute in place")
Signed-off-by: chenjie <chenjie6 at huawei.com>
Signed-off-by: guoxuenan <guoxuenan at huawei.com>
Acked-by: Michal Hocko <mhocko at suse.com>
Cc: Minchan Kim <minchan at kernel.org>
Cc: zhangyi (F) <yi.zhang at huawei.com>
Cc: Miao Xie <miaoxie at huawei.com>
Cc: Mike Rapoport <rppt at linux.vnet.ibm.com>
Cc: Shaohua Li <shli at fb.com>
Cc: Andrea Arcangeli <aarcange at redhat.com>
Cc: Mel Gorman <mgorman at techsingularity.net>
Cc: Kirill A. Shutemov <kirill.shutemov at linux.intel.com>
Cc: David Rientjes <rientjes at google.com>
Cc: Anshuman Khandual <khandual at linux.vnet.ibm.com>
Cc: Rik van Riel <riel at redhat.com>
Cc: Carsten Otte <cotte at de.ibm.com>
Cc: Dan Williams <dan.j.williams at intel.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
(cherry picked from commit 6ea8d958a2c95a1d514015d4e29ba21a8c0a1a91)
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
---
 mm/madvise.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 4edca1d86339..d968b9fc0a7e 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -264,15 +264,14 @@ static long madvise_willneed(struct vm_area_struct *vma,
 {
 	struct file *file = vma->vm_file;
 
+	*prev = vma;
 #ifdef CONFIG_SWAP
 	if (!file) {
-		*prev = vma;
 		force_swapin_readahead(vma, start, end);
 		return 0;
 	}
 
 	if (shmem_mapping(file->f_mapping)) {
-		*prev = vma;
 		force_shm_swapin_readahead(vma, start, end,
 					file->f_mapping);
 		return 0;
@@ -287,7 +286,6 @@ static long madvise_willneed(struct vm_area_struct *vma,
 		return 0;
 	}
 
-	*prev = vma;
 	start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 	if (end > vma->vm_end)
 		end = vma->vm_end;
-- 
2.14.1