mm/madvise.c: fix madvise() infinite loop under special circumstances

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@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@huawei.com>
Signed-off-by: guoxuenan <guoxuenan@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: zhangyi (F) <yi.zhang@huawei.com>
Cc: Miao Xie <miaoxie@huawei.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Carsten Otte <cotte@de.ibm.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 6ea8d958a2c95a1d514015d4e29ba21a8c0a1a91)
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Colin King <colin.king@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/mm/madvise.c b/mm/madvise.c
index 4edca1d863395d7f03abe12c213965bcf84ec3b3..d968b9fc0a7e437eba33f8eec716718b61c43b38 100644 (file)
--- 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;