We describe our reproducing workflow as following:
- Test input
We run 2 kernel test inputs in 2 kernel threads concurrently. They are generated by Syzkaller and attached below.
- Schedule execution
To schedule the execution of 2 threads, we leverage an academic research tool called SKI.
In general, we added a big big delay after the read access from do_mpage_readpage() happens and then we monitor if the write access from set_blocksize() also hits the same memory resource.
Test input 1
r0 = socket$inet6_udplite(0xa, 0x2, 0x88)
sendmmsg$inet6(r0, &(0x7f0000000980)=[{{&(0x7f0000000100)={0xa, 0x4e23, 0x0, @dev}, 0x1c, &(0x7f0000000880)=[{&(0x7f0000000140)='.', 0x1}, {&(0x7f0000000200)="18", 0x1}], 0x2, &(0x7f0000000940)=[@flowinfo={{0x14, 0x29, 0xb, 0x85e}}], 0x18}}], 0x1, 0x0)
sishuai@rssys-server:/data1/sishuai/experiment/test/corpus/test$ cat 14044
syz_mount_image$ext4(&(0x7f0000000000)='ext4\x00', &(0x7f0000000100)='./file0\x00', 0x100000, 0x19, &(0x7f0000000200)=[{&(0x7f0000010000)="200000000002000019000000900100000f000000000000000100000005000000000004000040000020000000dbf4655fdbf4655f0100ffff53ef010001000000daf4655f000000000000000001000000000000000b0000000001000018000000c28500002b0200000000000000000000000000000000000073797a6b616c6c6572000000000000002f746d702f73797a2d696d61676567656e32323330373039383000"/192, 0xc0, 0x400}, {&(0x7f0000010100)="000000000000000000000000e8f7d2e8feeb4bf889ba053b02420ff8010040000c00000000000000daf4655f00"/64, 0x40, 0x4e0}, {&(0x7f0000010200)="00000000000000000000000000000000000000000000000000000000200020000100000000000500400000000000000000000000000000004300000000000000", 0x40, 0x540}, {&(0x7f0000010300)="02000000030000000400000019000f0003000400"/32, 0x20, 0x800}, {&(0x7f0000010400)="7f000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff0100ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff0000000000000000daf4655fdaf4655fdaf4655f00"/4128, 0x1020, 0x1000}, {&(0x7f0000011500)="ed41000000080000daf4655fdbf4655fdbf4655f00000000000004004000000000000800050000000af301000400000000000000000000000100000010000000", 0x40, 0x2100}, {&(0x7f0000011600)="20000000641e8ebf641e8ebf00000000daf4655f00"/32, 0x20, 0x2180}, {&(0x7f0000011700)="8081000000601020daf4655fdaf4655fdaf4655f00000000000001004000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000030000000000000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000daf4655f00"/160, 0xa0, 0x2600}, {&(0x7f0000011800)="c041000000380000daf4655fdaf4655fdaf4655f00000000000002004000000000000800000000000af301000400000000000000000000000700000020000000", 0x40, 0x2a00}, {&(0x7f0000011900)="20000000000000000000000000000000daf4655f000000000000000000000000000002ea00"/64, 0x40, 0x2a80}, {&(0x7f0000011a00)="ed4100003c000000dbf4655fdbf4655fdbf4655f0000000000000200000000000000001003000000020000000d0000001000050166696c65300000000e0000002800050766696c6531000000000000000000000000000000000000000000000000000000904a5ec200000000000000000000000000000000000000000000000020000000641e8ebf641e8ebf641e8ebfdbf4655f641e8ebf0000000000000000000002ea04070000000000000000000000000000646174610000000000000000", 0xc0, 0x2b00}, {&(0x7f0000011b00)="ed8100001a040000dbf4655fdbf4655fdbf4655f00000000000001004000000000000800010000000af30100040000000000000000000000010000005000000000000000000000000000000000000000000000000000000000000000000000000000000046b58a6000000000000000000000000000000000000000000000000020000000641e8ebf641e8ebf641e8ebfdbf4655f641e8ebf0000000000000000", 0xa0, 0x2c00}, {&(0x7f0000011c00)="ffa1000026000000dbf4655fdbf4655fdbf4655f00000000000001000000000000000000010000002f746d702f73797a2d696d61676567656e3232333037303938302f66696c65302f66696c65300000000000000000000000000000000000000000000029d1c2e100000000000000000000000000000000000000000000000020000000641e8ebf641e8ebf641e8ebfdbf4655f641e8ebf0000000000000000", 0xa0, 0x2d00}, {&(0x7f0000011d00)="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", 0x1a0, 0x2e00}, {&(0x7f0000011f00)="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", 0x100, 0x3000}, {&(0x7f0000012000)="020000000c0001022e000000020000000c0002022e2e00000b00000014000a026c6f73742b666f756e6400000c0000001000050266696c65300000000f0000001000050166696c6531000000100000001000050166696c6532000000100000001000050166696c6533000000110000009407090166696c652e636f6c64000000", 0x80, 0x8000}, {&(0x7f0000012100)="0b0000000c0001022e000000020000000c0002022e2e000000000000e8070000", 0x20, 0x10000}, {&(0x7f0000012200)='\x00\x00\x00\x00\x00\b\x00'/32, 0x20, 0x10800}, {&(0x7f0000012300)='\x00\x00\x00\x00\x00\b\x00'/32, 0x20, 0x11000}, {&(0x7f0000012400)='\x00\x00\x00\x00\x00\b\x00'/32, 0x20, 0x11800}, {&(0x7f0000012500)='\x00\x00\x00\x00\x00\b\x00'/32, 0x20, 0x12000}, {&(0x7f0000012600)='\x00\x00\x00\x00\x00\b\x00'/32, 0x20, 0x12800}, {&(0x7f0000012700)='\x00\x00\x00\x00\x00\b\x00'/32, 0x20, 0x13000}, {&(0x7f0000012800)="504d4d00504d4dffdbf4655f00000000647679756b6f762d676c6170746f70320000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000006c6f6f7033320075782f746573742f73797a5f6d6f756e745f696d6167655f650500"/128, 0x80, 0x20000}, {&(0x7f0000012900)='syzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkallersyzkal\x00\x00\x00\x00\x00\x00', 0x420, 0x28000}], 0x0, &(0x7f0000012e00))
Test input 2
r0 = perf_event_open(&(0x7f0000000000)={0x0, 0x70, 0x3, 0x0, 0x0, 0x0, 0x0, 0xffffffff, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, @perf_config_ext}, 0x0, 0xffffffffffffffff, 0xffffffffffffffff, 0x0)
ioctl$PERF_EVENT_IOC_PERIOD(r0, 0x40082404, &(0x7f0000000080)=0x40)
syz_mount_image$ext4(&(0x7f0000000000)='ext4\x00', &(0x7f0000000100)='./file0\x00', 0x200000, 0x4, &(0x7f0000000200)=[{&(0x7f0000010000)="200000000002000019000000900100000f000000000000000200000006000000000008000080000020000000d6f4655fd6f4655f0100ffff53ef010001000000d5f4655f000000000000000001000000000000000b0000000001000018000000c28500002b02", 0x66, 0x400}, {&(0x7f0000010100)="00000000000000000000000028305c8a835f4f4da440baa59e2884cb010040", 0x1f, 0x4e0}, {&(0x7f0000010300)="020000000300000004", 0x9, 0x1000}, {&(0x7f0000012500)="ed41000000100000d5f4655fd6f4655f33f4655f000000000000040080000000f9ff", 0x22, 0x4100}], 0x1000085, &(0x7f0000000080)=ANY=[@ANYBLOB='\x00'])
umount2(&(0x7f0000000040)='./file0\x00', 0x0)
Thanks,
Sishuai
> On Nov 30, 2020, at 11:19 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>
> On Mon, Nov 30, 2020 at 04:10:42PM +0000, Matthew Wilcox wrote:
>> On Mon, Nov 30, 2020 at 03:41:53PM +0000, Gong, Sishuai wrote:
>>> We found a data race in linux kernel 5.3.11 that we are able to reproduce in x86 under specific interleavings. Currently, we are not sure about the consequence of this race so we would like to confirm with the community if this can be a harmful bug.
>>
>> How are you able to reproduce it? Normally mpage_readpage() is only called
>> from a filesystem, and you shouldn't be able to change the size of the
>> blocks in a block device while there's a mounted filesystem.
>
> mpage_readpages was also called by blkdev_readpages. For current
> mainline s/readpages/readahead/ but the effect should be the same.
