[syzbot] general protection fault in sg_alloc_append_table_from_pages

[syzbot <syzbot+2c56b725ec547fa9cb29@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    717478d89fe2 Merge tag 'riscv-for-linus-5.15-rc5' of git:/..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12489abf300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=32e6048063923b7b
dashboard link: https://syzkaller.appspot.com/bug?extid=2c56b725ec547fa9cb29
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=167b9e4f300000

The issue was bisected to:

commit 284562e1f34874e267d4f499362c3816f8f6bc3f
Author: Gurchetan Singh <gurchetansingh@chromium.org>
Date:   Tue Dec 3 01:36:27 2019 +0000

    udmabuf: implement begin_cpu_access/end_cpu_access hooks

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=12d68447300000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=11d68447300000
console output: https://syzkaller.appspot.com/x/log.txt?x=16d68447300000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2c56b725ec547fa9cb29@syzkaller.appspotmail.com
Fixes: 284562e1f348 ("udmabuf: implement begin_cpu_access/end_cpu_access hooks")

general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
CPU: 1 PID: 7990 Comm: syz-executor.0 Not tainted 5.15.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:sg_alloc_append_table_from_pages+0x821/0xdb0 lib/scatterlist.c:525
Code: 0c 24 48 8b 4c 24 48 48 39 c8 48 0f 46 c8 89 f0 4c 8d 3c c7 48 89 4c 24 30 48 b9 00 00 00 00 00 fc ff df 4c 89 f8 48 c1 e8 03 <80> 3c 08 00 0f 85 24 05 00 00 4d 8b 3f 4c 89 e0 31 ff 83 e0 03 48
RSP: 0018:ffffc90006087c48 EFLAGS: 00010212
RAX: 0000000000000002 RBX: 0000000000000001 RCX: dffffc0000000000
RDX: ffff888074588000 RSI: 0000000000000000 RDI: 0000000000000010
RBP: 00000000fffff000 R08: fffffffffffff000 R09: ffff88801afe1940
R10: ffffffff83d737d0 R11: 0000000000000000 R12: 0000000000000002
R13: ffff88801afe1940 R14: 0000000000000000 R15: 0000000000000010
FS:  00007fd273545700(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd273545718 CR3: 000000001a51c000 CR4: 0000000000350ee0
Call Trace:
 sg_alloc_table_from_pages_segment+0xc9/0x260 lib/scatterlist.c:573
 sg_alloc_table_from_pages include/linux/scatterlist.h:331 [inline]
 get_sg_table.isra.0+0xbb/0x160 drivers/dma-buf/udmabuf.c:67
 begin_cpu_udmabuf+0x130/0x1d0 drivers/dma-buf/udmabuf.c:126
 dma_buf_begin_cpu_access+0xfd/0x1d0 drivers/dma-buf/dma-buf.c:1204
 dma_buf_ioctl+0x29a/0x380 drivers/dma-buf/dma-buf.c:403
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl fs/ioctl.c:860 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7fd273e108d9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd273545188 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fd273f150e0 RCX: 00007fd273e108d9
RDX: 0000000020000000 RSI: 0000000040086200 RDI: 0000000000000004
RBP: 00007fd273e6acb4 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffd358e3ccf R14: 00007fd273545300 R15: 0000000000022000
Modules linked in:
---[ end trace 225c119d3f055d42 ]---
RIP: 0010:sg_alloc_append_table_from_pages+0x821/0xdb0 lib/scatterlist.c:525
Code: 0c 24 48 8b 4c 24 48 48 39 c8 48 0f 46 c8 89 f0 4c 8d 3c c7 48 89 4c 24 30 48 b9 00 00 00 00 00 fc ff df 4c 89 f8 48 c1 e8 03 <80> 3c 08 00 0f 85 24 05 00 00 4d 8b 3f 4c 89 e0 31 ff 83 e0 03 48
RSP: 0018:ffffc90006087c48 EFLAGS: 00010212
RAX: 0000000000000002 RBX: 0000000000000001 RCX: dffffc0000000000
RDX: ffff888074588000 RSI: 0000000000000000 RDI: 0000000000000010
RBP: 00000000fffff000 R08: fffffffffffff000 R09: ffff88801afe1940
R10: ffffffff83d737d0 R11: 0000000000000000 R12: 0000000000000002
R13: ffff88801afe1940 R14: 0000000000000000 R15: 0000000000000010
FS:  00007fd273545700(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd273545718 CR3: 000000001a51c000 CR4: 0000000000350ee0
----------------
Code disassembly (best guess):
   0:	0c 24                	or     $0x24,%al
   2:	48 8b 4c 24 48       	mov    0x48(%rsp),%rcx
   7:	48 39 c8             	cmp    %rcx,%rax
   a:	48 0f 46 c8          	cmovbe %rax,%rcx
   e:	89 f0                	mov    %esi,%eax
  10:	4c 8d 3c c7          	lea    (%rdi,%rax,8),%r15
  14:	48 89 4c 24 30       	mov    %rcx,0x30(%rsp)
  19:	48 b9 00 00 00 00 00 	movabs $0xdffffc0000000000,%rcx
  20:	fc ff df
  23:	4c 89 f8             	mov    %r15,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	80 3c 08 00          	cmpb   $0x0,(%rax,%rcx,1) <-- trapping instruction
  2e:	0f 85 24 05 00 00    	jne    0x558
  34:	4d 8b 3f             	mov    (%r15),%r15
  37:	4c 89 e0             	mov    %r12,%rax
  3a:	31 ff                	xor    %edi,%edi
  3c:	83 e0 03             	and    $0x3,%eax
  3f:	48                   	rex.W


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