[PATCH 4.0 007/220] net: fix crash in build_skb()

From: Greg Kroah-Hartman
Date: Sat May 02 2015 - 15:10:35 EST

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4.0-stable review patch. If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ Upstream commit 2ea2f62c8bda242433809c7f4e9eae1c52c40bbe ]

When I added pfmemalloc support in build_skb(), I forgot netlink
was using build_skb() with a vmalloc() area.

In this patch I introduce __build_skb() for netlink use,
and build_skb() is a wrapper handling both skb->head_frag and
skb->pfmemalloc

This means netlink no longer has to hack skb->head_frag

[ 1567.700067] kernel BUG at arch/x86/mm/physaddr.c:26!
[ 1567.700067] invalid opcode: 0000 [#1] PREEMPT SMP KASAN
[ 1567.700067] Dumping ftrace buffer:
[ 1567.700067] (ftrace buffer empty)
[ 1567.700067] Modules linked in:
[ 1567.700067] CPU: 9 PID: 16186 Comm: trinity-c182 Not tainted 4.0.0-next-20150424-sasha-00037-g4796e21 #2167
[ 1567.700067] task: ffff880127efb000 ti: ffff880246770000 task.ti: ffff880246770000
[ 1567.700067] RIP: __phys_addr (arch/x86/mm/physaddr.c:26 (discriminator 3))
[ 1567.700067] RSP: 0018:ffff8802467779d8 EFLAGS: 00010202
[ 1567.700067] RAX: 000041000ed8e000 RBX: ffffc9008ed8e000 RCX: 000000000000002c
[ 1567.700067] RDX: 0000000000000004 RSI: 0000000000000000 RDI: ffffffffb3fd6049
[ 1567.700067] RBP: ffff8802467779f8 R08: 0000000000000019 R09: ffff8801d0168000
[ 1567.700067] R10: ffff8801d01680c7 R11: ffffed003a02d019 R12: ffffc9000ed8e000
[ 1567.700067] R13: 0000000000000f40 R14: 0000000000001180 R15: ffffc9000ed8e000
[ 1567.700067] FS: 00007f2a7da3f700(0000) GS:ffff8801d1000000(0000) knlGS:0000000000000000
[ 1567.700067] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1567.700067] CR2: 0000000000738308 CR3: 000000022e329000 CR4: 00000000000007e0
[ 1567.700067] Stack:
[ 1567.700067] ffffc9000ed8e000 ffff8801d0168000 ffffc9000ed8e000 ffff8801d0168000
[ 1567.700067] ffff880246777a28 ffffffffad7c0a21 0000000000001080 ffff880246777c08
[ 1567.700067] ffff88060d302e68 ffff880246777b58 ffff880246777b88 ffffffffad9a6821
[ 1567.700067] Call Trace:
[ 1567.700067] build_skb (include/linux/mm.h:508 net/core/skbuff.c:316)
[ 1567.700067] netlink_sendmsg (net/netlink/af_netlink.c:1633 net/netlink/af_netlink.c:2329)
[ 1567.774369] ? sched_clock_cpu (kernel/sched/clock.c:311)
[ 1567.774369] ? netlink_unicast (net/netlink/af_netlink.c:2273)
[ 1567.774369] ? netlink_unicast (net/netlink/af_netlink.c:2273)
[ 1567.774369] sock_sendmsg (net/socket.c:614 net/socket.c:623)
[ 1567.774369] sock_write_iter (net/socket.c:823)
[ 1567.774369] ? sock_sendmsg (net/socket.c:806)
[ 1567.774369] __vfs_write (fs/read_write.c:479 fs/read_write.c:491)
[ 1567.774369] ? get_lock_stats (kernel/locking/lockdep.c:249)
[ 1567.774369] ? default_llseek (fs/read_write.c:487)
[ 1567.774369] ? vtime_account_user (kernel/sched/cputime.c:701)
[ 1567.774369] ? rw_verify_area (fs/read_write.c:406 (discriminator 4))
[ 1567.774369] vfs_write (fs/read_write.c:539)
[ 1567.774369] SyS_write (fs/read_write.c:586 fs/read_write.c:577)
[ 1567.774369] ? SyS_read (fs/read_write.c:577)
[ 1567.774369] ? __this_cpu_preempt_check (lib/smp_processor_id.c:63)
[ 1567.774369] ? trace_hardirqs_on_caller (kernel/locking/lockdep.c:2594 kernel/locking/lockdep.c:2636)
[ 1567.774369] ? trace_hardirqs_on_thunk (arch/x86/lib/thunk_64.S:42)
[ 1567.774369] system_call_fastpath (arch/x86/kernel/entry_64.S:261)

Fixes: 79930f5892e ("net: do not deplete pfmemalloc reserve")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/linux/skbuff.h | 1 +
net/core/skbuff.c | 31 ++++++++++++++++++++++---------
net/netlink/af_netlink.c | 6 ++----
3 files changed, 25 insertions(+), 13 deletions(-)

--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -769,6 +769,7 @@ bool skb_try_coalesce(struct sk_buff *to

struct sk_buff *__alloc_skb(unsigned int size, gfp_t priority, int flags,
int node);
+struct sk_buff *__build_skb(void *data, unsigned int frag_size);
struct sk_buff *build_skb(void *data, unsigned int frag_size);
static inline struct sk_buff *alloc_skb(unsigned int size,
gfp_t priority)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -280,13 +280,14 @@ nodata:
EXPORT_SYMBOL(__alloc_skb);

/**
- * build_skb - build a network buffer
+ * __build_skb - build a network buffer
* @data: data buffer provided by caller
- * @frag_size: size of fragment, or 0 if head was kmalloced
+ * @frag_size: size of data, or 0 if head was kmalloced
*
* Allocate a new &sk_buff. Caller provides space holding head and
* skb_shared_info. @data must have been allocated by kmalloc() only if
- * @frag_size is 0, otherwise data should come from the page allocator.
+ * @frag_size is 0, otherwise data should come from the page allocator
+ * or vmalloc()
* The return is the new skb buffer.
* On a failure the return is %NULL, and @data is not freed.
* Notes :
@@ -297,7 +298,7 @@ EXPORT_SYMBOL(__alloc_skb);
* before giving packet to stack.
* RX rings only contains data buffers, not full skbs.
*/
-struct sk_buff *build_skb(void *data, unsigned int frag_size)
+struct sk_buff *__build_skb(void *data, unsigned int frag_size)
{
struct skb_shared_info *shinfo;
struct sk_buff *skb;
@@ -311,11 +312,6 @@ struct sk_buff *build_skb(void *data, un

memset(skb, 0, offsetof(struct sk_buff, tail));
skb->truesize = SKB_TRUESIZE(size);
- if (frag_size) {
- skb->head_frag = 1;
- if (virt_to_head_page(data)->pfmemalloc)
- skb->pfmemalloc = 1;
- }
atomic_set(&skb->users, 1);
skb->head = data;
skb->data = data;
@@ -332,6 +328,23 @@ struct sk_buff *build_skb(void *data, un

return skb;
}
+
+/* build_skb() is wrapper over __build_skb(), that specifically
+ * takes care of skb->head and skb->pfmemalloc
+ * This means that if @frag_size is not zero, then @data must be backed
+ * by a page fragment, not kmalloc() or vmalloc()
+ */
+struct sk_buff *build_skb(void *data, unsigned int frag_size)
+{
+ struct sk_buff *skb = __build_skb(data, frag_size);
+
+ if (skb && frag_size) {
+ skb->head_frag = 1;
+ if (virt_to_head_page(data)->pfmemalloc)
+ skb->pfmemalloc = 1;
+ }
+ return skb;
+}
EXPORT_SYMBOL(build_skb);

struct netdev_alloc_cache {
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1616,13 +1616,11 @@ static struct sk_buff *netlink_alloc_lar
if (data == NULL)
return NULL;

- skb = build_skb(data, size);
+ skb = __build_skb(data, size);
if (skb == NULL)
vfree(data);
- else {
- skb->head_frag = 0;
+ else
skb->destructor = netlink_skb_destructor;
- }

return skb;
}

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Next message: Greg Kroah-Hartman: "[PATCH 4.0 008/220] pxa168: fix double deallocation of managed resources"
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