Remove broken ptrace() special-case code from file mapping

The kernel has for random historical reasons allowed ptrace() accesses
to access (and insert) pages into the page cache above the size of the
file.

However, Nick broke that by mistake when doing the new fault handling in
commit 54cb8821de07f2ffcd28c380ce9b93d5784b40d7 ("mm: merge populate and
nopage into fault (fixes nonlinear)".  The breakage caused a hang with
gdb when trying to access the invalid page.

The ptrace "feature" really isn't worth resurrecting, since it really is
wrong both from a portability _and_ from an internal page cache validity
standpoint.  So this removes those old broken remnants, and fixes the
ptrace() hang in the process.

Noticed and bisected by Duane Griffin, who also supplied a test-case
(quoth Nick: "Well that's probably the best bug report I've ever had,
thanks Duane!").

Cc: Duane Griffin <duaneg@dghda.com>
Acked-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/mm/filemap.c b/mm/filemap.c
index 15c8413ee929200006e4eb5e8a96bf5b04f0f213..14ca63f772ff8ea98097afed63c6c1e0570c784a 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1312,7 +1312,7 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 
        size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
        if (vmf->pgoff >= size)
-               goto outside_data_content;
+               return VM_FAULT_SIGBUS;
 
        /* If we don't want any read-ahead, don't bother */
        if (VM_RandomReadHint(vma))
@@ -1389,7 +1389,7 @@ retry_find:
        if (unlikely(vmf->pgoff >= size)) {
                unlock_page(page);
                page_cache_release(page);
-               goto outside_data_content;
+               return VM_FAULT_SIGBUS;
        }
 
        /*
@@ -1400,15 +1400,6 @@ retry_find:
        vmf->page = page;
        return ret | VM_FAULT_LOCKED;
 
-outside_data_content:
-       /*
-        * An external ptracer can access pages that normally aren't
-        * accessible..
-        */
-       if (vma->vm_mm == current->mm)
-               return VM_FAULT_SIGBUS;
-
-       /* Fall through to the non-read-ahead case */
 no_cached_page:
        /*
         * We're only likely to ever get here if MADV_RANDOM is in