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Subject[PATCH] block: tolerate tracing of NULL bio
Date
__get_request() can call trace_block_getrq() with bio=NULL which causes
block_get_rq::TP_fast_assign() to deref a NULL pointer and panic.

Syzkaller fuzzer panics with
linux-next (1d53d908b79d7870d89063062584eead4cf83448):
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
Modules linked in:
CPU: 0 PID: 2983 Comm: syzkaller401111 Not tainted 4.13.0-rc7-next-20170901+ #13
task: ffff8801cf1da000 task.stack: ffff8801ce440000
RIP: 0010:perf_trace_block_get_rq+0x697/0x970 include/trace/events/block.h:384
RSP: 0018:ffff8801ce4473f0 EFLAGS: 00010246
RAX: ffff8801cf1da000 RBX: 1ffff10039c88e84 RCX: 1ffffd1ffff84d27
RDX: dffffc0000000001 RSI: 1ffff1003b643e7a RDI: ffffe8ffffc26938
RBP: ffff8801ce447530 R08: 1ffff1003b643e6c R09: ffffe8ffffc26964
R10: 0000000000000002 R11: fffff91ffff84d2d R12: ffffe8ffffc1f890
R13: ffffe8ffffc26930 R14: ffffffff85cad9e0 R15: 0000000000000000
FS: 0000000002641880(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000043e670 CR3: 00000001d1d7a000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
trace_block_getrq include/trace/events/block.h:423 [inline]
__get_request block/blk-core.c:1283 [inline]
get_request+0x1518/0x23b0 block/blk-core.c:1355
blk_old_get_request block/blk-core.c:1402 [inline]
blk_get_request+0x1d8/0x3c0 block/blk-core.c:1427
sg_scsi_ioctl+0x117/0x750 block/scsi_ioctl.c:451
sg_ioctl+0x192d/0x2ed0 drivers/scsi/sg.c:1070
vfs_ioctl fs/ioctl.c:45 [inline]
do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:685
SYSC_ioctl fs/ioctl.c:700 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
entry_SYSCALL_64_fastpath+0x1f/0xbe

block_get_rq::TP_fast_assign() has multiple redundant ->dev assignments.
Only one of them is NULL tolerant. Favor the NULL tolerant one.

Fixes: 74d46992e0d9 ("block: replace bi_bdev with a gendisk pointer and partitions index")
Signed-off-by: Greg Thelen <gthelen@google.com>
---
include/trace/events/block.h | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/include/trace/events/block.h b/include/trace/events/block.h
index f815aaaef755..1fd7ff1a46f7 100644
--- a/include/trace/events/block.h
+++ b/include/trace/events/block.h
@@ -397,7 +397,6 @@ DECLARE_EVENT_CLASS(block_get_rq,

TP_fast_assign(
__entry->dev = bio ? bio_dev(bio) : 0;
- __entry->dev = bio_dev(bio);
__entry->sector = bio ? bio->bi_iter.bi_sector : 0;
__entry->nr_sector = bio ? bio_sectors(bio) : 0;
blk_fill_rwbs(__entry->rwbs,
@@ -414,7 +413,7 @@ DECLARE_EVENT_CLASS(block_get_rq,
/**
* block_getrq - get a free request entry in queue for block IO operations
* @q: queue for operations
- * @bio: pending block IO operation
+ * @bio: pending block IO operation (can be %NULL)
* @rw: low bit indicates a read (%0) or a write (%1)
*
* A request struct for queue @q has been allocated to handle the
@@ -430,7 +429,7 @@ DEFINE_EVENT(block_get_rq, block_getrq,
/**
* block_sleeprq - waiting to get a free request entry in queue for block IO operation
* @q: queue for operation
- * @bio: pending block IO operation
+ * @bio: pending block IO operation (can be %NULL)
* @rw: low bit indicates a read (%0) or a write (%1)
*
* In the case where a request struct cannot be provided for queue @q
--
2.14.1.581.gf28d330327-goog
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