mapping->host can be NULL and shouldn't be dereferenced before being checked.
[ 1295.741844] GPF could be caused by NULL-ptr deref or user memory accessgeneral protection fault: 0000 [#1] SMP KASAN
[ 1295.746387] Dumping ftrace buffer:
[ 1295.748217] (ftrace buffer empty)
[ 1295.749527] Modules linked in:
[ 1295.750268] CPU: 62 PID: 23410 Comm: trinity-c70 Not tainted 3.19.0-next-20150219-sasha-00045-g9130270f #1939
[ 1295.750268] task: ffff8803a49db000 ti: ffff8803a4dc8000 task.ti: ffff8803a4dc8000
[ 1295.750268] RIP: shmem_mapping (mm/shmem.c:1458)
[ 1295.750268] RSP: 0000:ffff8803a4dcfbf8 EFLAGS: 00010206
[ 1295.750268] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 00000000000f2804
[ 1295.750268] RDX: 0000000000000005 RSI: 0400000000000794 RDI: 0000000000000028
[ 1295.750268] RBP: ffff8803a4dcfc08 R08: 0000000000000000 R09: 00000000031de000
[ 1295.750268] R10: dffffc0000000000 R11: 00000000031c1000 R12: 0400000000000794
[ 1295.750268] R13: 00000000031c2000 R14: 00000000031de000 R15: ffff880e3bdc1000
[ 1295.750268] FS: 00007f8703c7e700(0000) GS:ffff881164800000(0000) knlGS:0000000000000000
[ 1295.750268] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1295.750268] CR2: 0000000004e58000 CR3: 00000003a9f3c000 CR4: 00000000000007a0
[ 1295.750268] DR0: ffffffff81000000 DR1: 0000009494949494 DR2: 0000000000000000
[ 1295.750268] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 00000000000d0602
[ 1295.750268] Stack:
[ 1295.750268] ffff8803a4dcfec8 ffffffffbb1dc770 ffff8803a4dcfc38 ffffffffad6f230b
[ 1295.750268] ffffffffad6f2b0d 0000014100000000 ffff88001e17c08b ffff880d9453fe08
[ 1295.750268] ffff8803a4dcfd18 ffffffffad6f2ce2 ffff8803a49dbcd8 ffff8803a49dbce0
[ 1295.750268] Call Trace:
[ 1295.750268] mincore_page (mm/mincore.c:61)
[ 1295.750268] ? mincore_pte_range (include/linux/spinlock.h:312 mm/mincore.c:131)
[ 1295.750268] mincore_pte_range (mm/mincore.c:151)
[ 1295.750268] ? mincore_unmapped_range (mm/mincore.c:113)
[ 1295.750268] __walk_page_range (mm/pagewalk.c:51 mm/pagewalk.c:90 mm/pagewalk.c:116 mm/pagewalk.c:204)
[ 1295.750268] walk_page_range (mm/pagewalk.c:275)
[ 1295.750268] SyS_mincore (mm/mincore.c:191 mm/mincore.c:253 mm/mincore.c:220)
[ 1295.750268] ? mincore_pte_range (mm/mincore.c:220)
[ 1295.750268] ? mincore_unmapped_range (mm/mincore.c:113)
[ 1295.750268] ? __mincore_unmapped_range (mm/mincore.c:105)
[ 1295.750268] ? ptlock_free (mm/mincore.c:24)
[ 1295.750268] ? syscall_trace_enter (arch/x86/kernel/ptrace.c:1610)
[ 1295.750268] ia32_do_call (arch/x86/ia32/ia32entry.S:446)
[ 1295.750268] Code: e5 48 c1 ea 03 53 48 89 fb 48 83 ec 08 80 3c 02 00 75 4f 48 b8 00 00 00 00 00 fc ff df 48 8b 1b 48 8d 7b 28 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 3f 48 b8 00 00 00 00 00 fc ff df 48 8b 5b 28 48
All code
========
0: e5 48 in $0x48,%eax
2: c1 ea 03 shr $0x3,%edx
5: 53 push %rbx
6: 48 89 fb mov %rdi,%rbx
9: 48 83 ec 08 sub $0x8,%rsp
d: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1)
11: 75 4f jne 0x62
13: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
1a: fc ff df
1d: 48 8b 1b mov (%rbx),%rbx
20: 48 8d 7b 28 lea 0x28(%rbx),%rdi
24: 48 89 fa mov %rdi,%rdx
27: 48 c1 ea 03 shr $0x3,%rdx
2b:* 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1) <-- trapping instruction
2f: 75 3f jne 0x70
31: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
38: fc ff df
3b: 48 8b 5b 28 mov 0x28(%rbx),%rbx
3f: 48 rex.W
...
Code starting with the faulting instruction
===========================================
0: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1)
4: 75 3f jne 0x45
6: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
d: fc ff df
10: 48 8b 5b 28 mov 0x28(%rbx),%rbx
14: 48 rex.W
...
[ 1295.750268] RIP shmem_mapping (mm/shmem.c:1458)
[ 1295.750268] RSP <ffff8803a4dcfbf8>
Fixes: 97b713ba3e ("fs: kill BDI_CAP_SWAP_BACKED")
Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
---
mm/shmem.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/mm/shmem.c b/mm/shmem.c
index 35843667..7f6f6d9 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1455,6 +1455,9 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
bool shmem_mapping(struct address_space *mapping)
{
+ if (!mapping->host)
+ return false;
+
return mapping->host->i_sb->s_op == &shmem_ops;
}
--
1.7.10.4
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