Re: [PATCH] net: arcnet: Fix a possible concurrency use-after-free bug in arcnet_reply_tasklet()

[kbuild test robot]

Hi Jia-Ju,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on net-next/master]
[also build test ERROR on v4.20 next-20181224]
[if your patch is applied to the wrong git tree, please drop us a note to help 
improve the system]

url:
https://github.com/0day-ci/linux/commits/Jia-Ju-Bai/net-arcnet-Fix-a-possible-concurrency-use-after-free-bug-in-arcnet_reply_tasklet/20181227-020417
config: x86_64-randconfig-x005-201851 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
# save the attached .config to linux build tree
make ARCH=x86_64 

All error/warnings (new ones prefixed by >>):

   In file included from include/linux/kernel.h:13:0,
from include/linux/list.h:9,
from include/linux/module.h:9,
from drivers/net/arcnet/arcnet.c:46:
   drivers/net/arcnet/arcnet.c: In function 'arcnet_reply_tasklet':
>> drivers/net/arcnet/arcnet.c:429:31: error: 'flags' undeclared (first use in 
>> this function); did you mean 'class'?
 spin_lock_irqsave(>lock, flags);
  ^
   include/linux/typecheck.h:11:9: note: in definition of macro 'typecheck'
 typeof(x) __dummy2; \
^
>> include/linux/spinlock.h:359:2: note: in expansion of macro 
>> 'raw_spin_lock_irqsave'
 raw_spin_lock_irqsave(spinlock_check(lock), flags); \
 ^
>> drivers/net/arcnet/arcnet.c:429:2: note: in expansion of macro 
>> 'spin_lock_irqsave'
 spin_lock_irqsave(>lock, flags);
 ^
   drivers/net/arcnet/arcnet.c:429:31: note: each undeclared identifier is 
reported only once for each function it appears in
 spin_lock_irqsave(>lock, flags);
  ^
   include/linux/typecheck.h:11:9: note: in definition of macro 'typecheck'
 typeof(x) __dummy2; \
^
>> include/linux/spinlock.h:359:2: note: in expansion of macro 
>> 'raw_spin_lock_irqsave'
 raw_spin_lock_irqsave(spinlock_check(lock), flags); \
 ^
>> drivers/net/arcnet/arcnet.c:429:2: note: in expansion of macro 
>> 'spin_lock_irqsave'
 spin_lock_irqsave(>lock, flags);
 ^
>> include/linux/typecheck.h:12:18: warning: comparison of distinct pointer 
>> types lacks a cast
 (void)(&__dummy == &__dummy2); \
 ^
>> include/linux/spinlock.h:240:3: note: in expansion of macro 'typecheck'
  typecheck(unsigned long, flags); \
  ^
>> include/linux/spinlock.h:359:2: note: in expansion of macro 
>> 'raw_spin_lock_irqsave'
 raw_spin_lock_irqsave(spinlock_check(lock), flags); \
 ^
>> drivers/net/arcnet/arcnet.c:429:2: note: in expansion of macro 
>> 'spin_lock_irqsave'
 spin_lock_irqsave(>lock, flags);
 ^
--
   In file included from include/linux/kernel.h:13:0,
from include/linux/list.h:9,
from include/linux/module.h:9,
from drivers/net//arcnet/arcnet.c:46:
   drivers/net//arcnet/arcnet.c: In function 'arcnet_reply_tasklet':
   drivers/net//arcnet/arcnet.c:429:31: error: 'flags' undeclared (first use in 
this function); did you mean 'class'?
 spin_lock_irqsave(>lock, flags);
  ^
   include/linux/typecheck.h:11:9: note: in definition of macro 'typecheck'
 typeof(x) __dummy2; \
^
>> include/linux/spinlock.h:359:2: note: in expansion of macro 
>> 'raw_spin_lock_irqsave'
 raw_spin_lock_irqsave(spinlock_check(lock), flags); \
 ^
   drivers/net//arcnet/arcnet.c:429:2: note: in expansion of macro 
'spin_lock_irqsave'
 spin_lock_irqsave(>lock, flags);
 ^
   drivers/net//arcnet/arcnet.c:429:31: note: each undeclared identifier is 
reported only once for each function it appears in
 spin_lock_irqsave(>lock, flags);
  ^
   include/linux/typecheck.h:11:9: note: in definition of macro 'typecheck'
 typeof(x) __dummy2; \
^
>> include/linux/spinlock.h:359:2: note: in expansion of macro 
>> 'raw_spin_lock_irqsave'
 raw_spin_lock_irqsave(spinlock_check(lock), flags); \
 ^
   drivers/net//arcnet/arcnet.c:429:2: note: in expansion of macro 
'spin_lock_irqsave'
 spin_lock_irqsave(>lock, flags);
 ^
>> include/linux/typecheck.h:12:18: warning: comparison of distinct pointer 
>> types lacks a cast
 (void)(&__dummy == &__dummy2); \
 ^
>> include/linux/spinlock.h:240:3: note: in expansion of macro 'typecheck'
  typecheck(unsigned long, flags); \
  ^
>> include/linux/spinlock.h:359:2: note: in expansion of macro 
>> 'raw_spin_lock_irqsave'
 raw_spin_lock_irqsave(spinlock_check(lock), flags); \
 ^
   drivers/net//arcnet/arcnet.c:429:2: note: in expansion of macro 
'spin_lock_irqsave'
 spin_lock_irqsave(>lock, flags);
 

[PATCH] net: arcnet: Fix a possible concurrency use-after-free bug in arcnet_reply_tasklet()

[Jia-Ju Bai]

In drivers/net/arcnet/arcnet.c, the functions arcnet_reply_tasklet() and
arcnet_send_packet() may be concurrently executed.

arcnet_reply_tasklet()
  line 430: dev_kfree_skb(lp->outgoing.skb);

arcnet_send_packet()
  line 682: spin_lock_irqsave();
  line 690: lp->outgoing.skb = skb;
  line 691: proto->prepare_tx(..., skb->len, ...)

Thus, a possible concurrency use-after-free bugs may occur.

To fix this bug, the calls to spin_lock_irqsave() and
spin_unlock_irqrestore() are added in arcnet_reply_tasklet() to protect
dev_kfree_skb(lp->outgoing.skb).

Signed-off-by: Jia-Ju Bai 
---
 drivers/net/arcnet/arcnet.c | 4 
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/arcnet/arcnet.c b/drivers/net/arcnet/arcnet.c
index 8459115d9d4e..c5e943d01d66 100644
--- a/drivers/net/arcnet/arcnet.c
+++ b/drivers/net/arcnet/arcnet.c
@@ -426,10 +426,14 @@ static void arcnet_reply_tasklet(unsigned long data)
serr->ee.ee_data = skb_shinfo(skb)->tskey;
serr->ee.ee_info = lp->reply_status;
 
+   spin_lock_irqsave(>lock, flags);
+
/* finally erasing outgoing skb */
dev_kfree_skb(lp->outgoing.skb);
lp->outgoing.skb = NULL;
 
+   spin_unlock_irqrestore(>lock, flags);
+
ackskb->dev = lp->dev;
 
ret = sock_queue_err_skb(sk, ackskb);
-- 
2.17.0