The patch titled
Subject: netvm: check for page == NULL when propagating the skb->pfmemalloc flag
has been added to the -mm tree. Its filename is
netvm-check-for-page-==-null-when-propagating-the-skb-pfmemalloc-flag.patch
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------------------------------------------------------
From: Mel Gorman <mgorman@xxxxxxx>
Subject: netvm: check for page == NULL when propagating the skb->pfmemalloc flag
Commit c48a11c7 ("netvm: propagate page->pfmemalloc to skb") is
responsible for the following bug triggered by a xen network driver
[ 1.908592] BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
[ 1.908643] IP: [<ffffffffa0037750>] xennet_poll+0x980/0xec0 [xen_netfront]
[ 1.908703] PGD ea1df067 PUD e8ada067 PMD 0
[ 1.908774] Oops: 0000 [#1] SMP
[ 1.908797] Modules linked in: fbcon tileblit font radeon bitblit softcursor ttm drm_kms_helper crc32c_intel xen_blkfront xen_netfront xen_fbfront fb_sys_fops sysimgblt sysfillrect syscopyarea +xen_kbdfront xenfs xen_privcmd
[ 1.908938] CPU 0
[ 1.908950] Pid: 2165, comm: ip Not tainted 3.5.0upstream-08854-g444fa66 #1
[ 1.908983] RIP: e030:[<ffffffffa0037750>] [<ffffffffa0037750>] xennet_poll+0x980/0xec0 [xen_netfront]
[ 1.909029] RSP: e02b:ffff8800ffc03db8 EFLAGS: 00010282
[ 1.909055] RAX: ffff8800ea010140 RBX: ffff8800f00e86c0 RCX: 000000000000009a
[ 1.909055] RDX: 0000000000000040 RSI: 000000000000005a RDI: ffff8800fa7dee80
[ 1.909055] RBP: ffff8800ffc03ee8 R08: ffff8800f00e86d8 R09: ffff8800ea010000
[ 1.909055] R10: dead000000200200 R11: dead000000100100 R12: ffff8800fa7dee80
[ 1.909055] R13: 000000000000005a R14: ffff8800fa7dee80 R15: 0000000000000200
[ 1.909055] FS: 00007fbafc188700(0000) GS:ffff8800ffc00000(0000) knlGS:0000000000000000
[ 1.909055] CS: e033 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 1.909055] CR2: 0000000000000010 CR3: 00000000ea108000 CR4: 0000000000002660
[ 1.909055] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1.909055] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[ 1.909055] Process ip (pid: 2165, threadinfo ffff8800ea0f2000, task ffff8800fa783040)
[ 1.909055] Stack:
[ 1.909055] ffff8800e27e5040 ffff8800ffc03e88 ffff8800ffc03e68 ffff8800ffc03e48
[ 1.909055] 7fffffffffffffff ffff8800ffc03e00 ffff8800e27e5040 ffff8800f00e86d8
[ 1.909055] ffff8800ffc03eb0 00000040ffffffff ffff8800f00e8000 00000000ffc03e30
[ 1.909055] Call Trace:
[ 1.909055] <IRQ>
[ 1.909055] [<ffffffff81066028>] ? pvclock_clocksource_read+0x58/0xd0
[ 1.909055] [<ffffffff81486352>] net_rx_action+0x112/0x240
[ 1.909055] [<ffffffff8107f319>] __do_softirq+0xb9/0x190
[ 1.909055] [<ffffffff815d8d7c>] call_softirq+0x1c/0x30
The problem is that the xenfront driver is passing a NULL page to
__skb_fill_page_desc() which was unexpected. This patch checks that there
is a page before dereferencing.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Cc: David Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/skbuff.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN include/linux/skbuff.h~netvm-check-for-page-==-null-when-propagating-the-skb-pfmemalloc-flag include/linux/skbuff.h
--- a/include/linux/skbuff.h~netvm-check-for-page-==-null-when-propagating-the-skb-pfmemalloc-flag
+++ a/include/linux/skbuff.h
@@ -1259,7 +1259,7 @@ static inline void __skb_fill_page_desc(
* do not lose pfmemalloc information as the pages would not be
* allocated using __GFP_MEMALLOC.
*/
- if (page->pfmemalloc && !page->mapping)
+ if (page && page->pfmemalloc && !page->mapping)
skb->pfmemalloc = true;
frag->page.p = page;
frag->page_offset = off;
_
Patches currently in -mm which might be from mgorman@xxxxxxx are
linux-next.patch
mm-hugetlbfs-correctly-populate-shared-pmd.patch
mm-hugetlbfs-correctly-populate-shared-pmd-fix.patch
alpha-redefine-atomic_init-and-atomic64_init-to-drop-the-casts.patch
netvm-check-for-page-==-null-when-propagating-the-skb-pfmemalloc-flag.patch
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