On 12.01.2016 00:11, Salam Noureddine wrote:
Would you be able to disassemble your kernel so we could tell where
the null pointer dereference happens?
Sure, but wouldn't it be better to provide the object file containing
the debug symbols as well?
Otherwise, the null pointer dereference happens somewhere in:
(gdb) l *__netif_receive_skb_core+0x7c0
0x1318 is in __netif_receive_skb_core (include/linux/compiler.h:218).
213 })
214
215 static __always_inline
216 void __read_once_size(const volatile void *p, void *res, int size)
217 {
218 __READ_ONCE_SIZE;
219 }
220
221 #ifdef CONFIG_KASAN
222 /*
(gdb) l *__netif_receive_skb_core+0x7bc
0x1314 is in __netif_receive_skb_core (net/core/dev.c:3934).
3929 }
3930
3931 deliver_ptype_list_skb(skb, &pt_prev, orig_dev, type,
3932 &orig_dev->ptype_specific);
3933
3934 if (unlikely(skb->dev != orig_dev)) {
3935 deliver_ptype_list_skb(skb, &pt_prev, orig_dev, type,
3936 &skb->dev->ptype_specific);
3937 }
3938
(gdb) l *__netif_receive_skb_core+0x7c4
0x131c is in __netif_receive_skb_core (net/core/dev.c:3935).
3930
3931 deliver_ptype_list_skb(skb, &pt_prev, orig_dev, type,
3932 &orig_dev->ptype_specific);
3933
3934 if (unlikely(skb->dev != orig_dev)) {
3935 deliver_ptype_list_skb(skb, &pt_prev, orig_dev, type,
3936 &skb->dev->ptype_specific);
3937 }
3938
3939 if (pt_prev) {
0x00001300 <+1960>: cmp r10, r3
0x00001304 <+1964>: bne 0x1284 <__netif_receive_skb_core+1836>
0x00001308 <+1968>: ldr r4, [sp, #12]
0x0000130c <+1972>: ldr r3, [r4, #20]
0x00001310 <+1976>: cmp r3, r6
0x00001314 <+1980>: beq 0x13b0 <__netif_receive_skb_core+2136>
0x00001318 <+1984>: ldr r5, [r3, #92] ; 0x5c <-FAULT
r3 seems to be skb->dev
0x0000131c <+1988>: add r10, r3, #92 ; 0x5c
0x00001320 <+1992>: add r8, r4, #180 ; 0xb4
0x00001324 <+1996>: sub r5, r5, #20
0x00001328 <+2000>: b 0x13a4 <__netif_receive_skb_core+2124>
0x0000132c <+2004>: ldrh r3, [r5]
0x00001330 <+2008>: cmp r3, r7
I put some additional printks around that code, and it turned out that
skb->dev is null, so "if (unlikely(skb->dev != orig_dev))" succeeds, but
"&skb->dev->ptype_specific" oopses.
Thanks,
Ivo
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