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author | Andrea Arcangeli <aarcange@redhat.com> | 2017-06-02 23:46:11 +0200 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-06-03 00:07:37 +0200 |
commit | a7306c3436e9c8e584a4b9fad5f3dc91be2a6076 (patch) | |
tree | 5be4925ead3c94753bec62c7afcbf5472f6f0e7b /mm | |
parent | Merge tag 'sound-4.12-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/t... (diff) | |
download | linux-a7306c3436e9c8e584a4b9fad5f3dc91be2a6076.tar.xz linux-a7306c3436e9c8e584a4b9fad5f3dc91be2a6076.zip |
ksm: prevent crash after write_protect_page fails
"err" needs to be left set to -EFAULT if split_huge_page succeeds.
Otherwise if "err" gets clobbered with zero and write_protect_page
fails, try_to_merge_one_page() will succeed instead of returning -EFAULT
and then try_to_merge_with_ksm_page() will continue thinking kpage is a
PageKsm when in fact it's still an anonymous page. Eventually it'll
crash in page_add_anon_rmap.
This has been reproduced on Fedora25 kernel but I can reproduce with
upstream too.
The bug was introduced in commit f765f540598a ("ksm: prepare to new THP
semantics") introduced in v4.5.
page:fffff67546ce1cc0 count:4 mapcount:2 mapping:ffffa094551e36e1 index:0x7f0f46673
flags: 0x2ffffc0004007c(referenced|uptodate|dirty|lru|active|swapbacked)
page dumped because: VM_BUG_ON_PAGE(!PageLocked(page))
page->mem_cgroup:ffffa09674bf0000
------------[ cut here ]------------
kernel BUG at mm/rmap.c:1222!
CPU: 1 PID: 76 Comm: ksmd Not tainted 4.9.3-200.fc25.x86_64 #1
RIP: do_page_add_anon_rmap+0x1c4/0x240
Call Trace:
page_add_anon_rmap+0x18/0x20
try_to_merge_with_ksm_page+0x50b/0x780
ksm_scan_thread+0x1211/0x1410
? prepare_to_wait_event+0x100/0x100
? try_to_merge_with_ksm_page+0x780/0x780
kthread+0xd9/0xf0
? kthread_park+0x60/0x60
ret_from_fork+0x25/0x30
Fixes: f765f54059 ("ksm: prepare to new THP semantics")
Link: http://lkml.kernel.org/r/20170513131040.21732-1-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reported-by: Federico Simoncelli <fsimonce@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r-- | mm/ksm.c | 3 |
1 files changed, 1 insertions, 2 deletions
@@ -1028,8 +1028,7 @@ static int try_to_merge_one_page(struct vm_area_struct *vma, goto out; if (PageTransCompound(page)) { - err = split_huge_page(page); - if (err) + if (split_huge_page(page)) goto out_unlock; } |