UBSAN: Undefined behaviour in mm/fadvise.c

UBSAN: Undefined behaviour in mm/fadvise.c

[air icy]

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Hi,
This bug was found in Linux Kernel v4.18-rc2

 75         /* Careful about overflows. Len == 0 means "as much as possible" */
 76         endbyte = offset + len;
 77         if (!len || endbyte < len)
 78                 endbyte = -1;
 79         else
 80                 endbyte--;              /* inclusive */

$ cat report0
================================================================================
UBSAN: Undefined behaviour in mm/fadvise.c:76:10
signed integer overflow:
4 + 9223372036854775805 cannot be represented in type 'long long int'
CPU: 0 PID: 13477 Comm: syz-executor1 Not tainted 4.18.0-rc1 #2
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x122/0x1c8 lib/dump_stack.c:113
 ubsan_epilogue+0x12/0x86 lib/ubsan.c:159
 handle_overflow+0x1c2/0x21f lib/ubsan.c:190
 __ubsan_handle_add_overflow+0x2a/0x31 lib/ubsan.c:198
 ksys_fadvise64_64+0xbf0/0xd10 mm/fadvise.c:76
 __do_sys_fadvise64 mm/fadvise.c:198 [inline]
 __se_sys_fadvise64 mm/fadvise.c:196 [inline]
 __x64_sys_fadvise64+0xa9/0x120 mm/fadvise.c:196
 do_syscall_64+0xb8/0x3a0 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455a09
Code: 1d ba fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fc2de8f2c68 EFLAGS: 00000246 ORIG_RAX: 00000000000000dd
RAX: ffffffffffffffda RBX: 00007fc2de8f36d4 RCX: 0000000000455a09
RDX: 7ffffffffffffffd RSI: 0000000000000004 RDI: 0000000000000013
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000004 R11: 0000000000000246 R12: 00000000ffffffff
R13: 000000000000007d R14: 00000000006f5c58 R15: 0000000000000000
================================================================================
This bug can be repro, if you need it, please tell me.

bugzilla url: https://bugzilla.kernel.org/show_bug.cgi?id=200209
Thanks,
Icytxw

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