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lkmpg/examples
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linD026 c7a7a667cf
Avoid strlen by assigning explicit length of string for proc_read (#18) 
Since the address of buffer is userspace address, it may trigger an unexpected fault on strlen(buffer).

On Ubuntu 20.04.2 LTS ( 5.8.0-63-generic ), using strlen(buffer) will result in the following:
[ 2168.010930] /proc/buffer1k created
[ 2177.014347] BUG: unable to handle page fault for address: 00007fbbc2a17000
[ 2177.014355] #PF: supervisor read access in kernel mode
[ 2177.014358] #PF: error_code(0x0000) - not-present page
[ 2177.014361] PGD 80000003c61d0067 P4D 80000003c61d0067 PUD 3ee6c5067 PMD 40e1ff067 PTE 0
[ 2177.014369] Oops: 0000 [#1] SMP PTI
[ 2177.014376] CPU: 7 PID: 4750 Comm: cat Tainted: P        W  OE     5.8.0-63-generic #71~20.04.1-Ubuntu

[ 2177.014387] RIP: 0010:procfile_read+0xb/0x20 [procfs2]
[ 2177.014393] Code: Unable to access opcode bytes at RIP 0xffffffffc1253fe1.
[ 2177.014396] RSP: 0018:ffffbc84412cbe78 EFLAGS: 00010286
[ 2177.014400] RAX: ffffffffc1254000 RBX: 0000000000020000 RCX: ffffbc84412cbef0
[ 2177.014403] RDX: 0000000000020000 RSI: 00007fbbc2a17000 RDI: ffffa057d2708f00
[ 2177.014406] RBP: ffffbc84412cbe80 R08: 0000000000000001 R09: 0000000000000000
[ 2177.014409] R10: 0000000000000000 R11: 0000000000000000 R12: ffffa0581de8ccc0
[ 2177.014411] R13: ffffa057d2708f00 R14: ffffbc84412cbef0 R15: 00007fbbc2a17000
[ 2177.014415] FS:  00007fbbc3bfa580(0000) GS:ffffa0582dbc0000(0000) knlGS:0000000000000000
[ 2177.014418] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2177.014421] CR2: ffffffffc1253fe1 CR3: 00000003c611c004 CR4: 00000000003606e0
[ 2177.014424] Call Trace:
[ 2177.014435]  proc_reg_read+0x66/0x90
[ 2177.014441]  vfs_read+0xaa/0x190
[ 2177.014446]  ksys_read+0x67/0xe0
[ 2177.014451]  __x64_sys_read+0x1a/0x20
[ 2177.014458]  do_syscall_64+0x49/0xc0
[ 2177.014464]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 2177.014467] RIP: 0033:0x7fbbc3b18142
[ 2177.014472] Code: c0 e9 c2 fe ff ff 50 48 8d 3d 3a ca 0a 00 e8 f5 19 02 00 0f 1f 44 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 0f 05 <48> 3d 00 f0 ff ff 77 56 c3 0f 1f 44 00 00 48 83 ec 28 48 89 54 24
[ 2177.014476] RSP: 002b:00007ffcf2d20d78 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[ 2177.014479] RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007fbbc3b18142
[ 2177.014482] RDX: 0000000000020000 RSI: 00007fbbc2a17000 RDI: 0000000000000003
[ 2177.014485] RBP: 00007fbbc2a17000 R08: 00007fbbc2a16010 R09: 0000000000000000
[ 2177.014487] R10: 0000000000000022 R11: 0000000000000246 R12: 0000560f8ff081f0
[ 2177.014490] R13: 0000000000000003 R14: 0000000000020000 R15: 0000000000020000

[ 2177.014635] CR2: 00007fbbc2a17000
[ 2177.014639] ---[ end trace b71ff05c1b0a10f6 ]---
[ 2177.184174] RIP: 0010:procfile_read+0xb/0x20 [procfs2]
[ 2177.184176] Code: Unable to access opcode bytes at RIP 0xffffffffc1253fe1.
[ 2177.184177] RSP: 0018:ffffbc84412cbe78 EFLAGS: 00010286
[ 2177.184178] RAX: ffffffffc1254000 RBX: 0000000000020000 RCX: ffffbc84412cbef0
[ 2177.184179] RDX: 0000000000020000 RSI: 00007fbbc2a17000 RDI: ffffa057d2708f00
[ 2177.184180] RBP: ffffbc84412cbe80 R08: 0000000000000001 R09: 0000000000000000
[ 2177.184180] R10: 0000000000000000 R11: 0000000000000000 R12: ffffa0581de8ccc0
[ 2177.184181] R13: ffffa057d2708f00 R14: ffffbc84412cbef0 R15: 00007fbbc2a17000
[ 2177.184182] FS:  00007fbbc3bfa580(0000) GS:ffffa0582dbc0000(0000) knlGS:0000000000000000
[ 2177.184182] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2177.184183] CR2: ffffffffc1253fe1 CR3: 00000003c611c004 CR4: 00000000003606e0
2021-07-29 16:10:52 +08:00
..
other Make each source file more consistent 2021-07-22 11:25:32 +08:00
.clang-format Enforce the customized style for example code 2021-07-22 06:58:13 +08:00
bottomhalf.c Make each source file more consistent 2021-07-22 11:25:32 +08:00
chardev.c Improve the compatibility with kernel version < 5.6 2021-07-22 07:17:31 +08:00
chardev.h Make each source file more consistent 2021-07-22 11:25:32 +08:00
chardev2.c Shorten sample code 2021-07-22 10:55:14 +08:00
completions.c Make each source file more consistent 2021-07-22 11:25:32 +08:00
cryptosha256.c Make each source file more consistent 2021-07-22 11:25:32 +08:00
cryptosk.c Make each source file more consistent 2021-07-22 11:25:32 +08:00
devicemodel.c Fix trivial tweak for missing comma 2021-07-26 03:08:27 +08:00
example_atomic.c Make each source file more consistent 2021-07-22 11:25:32 +08:00
example_mutex.c Make each source file more consistent 2021-07-22 11:25:32 +08:00
example_rwlock.c Make each source file more consistent 2021-07-22 11:25:32 +08:00
example_spinlock.c Make each source file more consistent 2021-07-22 11:25:32 +08:00
example_tasklet.c Make each source file more consistent 2021-07-22 11:25:32 +08:00
hello-1.c Enforce the customized style for example code 2021-07-22 06:58:13 +08:00
hello-2.c Enforce the customized style for example code 2021-07-22 06:58:13 +08:00
hello-3.c Enforce the customized style for example code 2021-07-22 06:58:13 +08:00
hello-4.c Drop duplicated module author information 2021-07-22 07:29:07 +08:00
hello-5.c Drop duplicated module author information 2021-07-22 07:29:07 +08:00
hello-sysfs.c Make each source file more consistent 2021-07-22 11:25:32 +08:00
intrpt.c Drop duplicated copyright notice 2021-07-22 10:53:45 +08:00
ioctl.c Make each source file more consistent 2021-07-22 11:25:32 +08:00
kbleds.c Drop duplicated module author information 2021-07-22 07:29:07 +08:00
Makefile Emphasize on 5.x kernel 2021-07-22 08:31:47 +08:00
print_string.c Remove linux-2.6 specific checks 2021-07-22 07:33:27 +08:00
procfs1.c Avoid strlen by assigning explicit length of string for proc_read (#18) 2021-07-29 16:10:52 +08:00
procfs2.c Avoid strlen by assigning explicit length of string for proc_read (#18) 2021-07-29 16:10:52 +08:00
procfs3.c Make each source file more consistent 2021-07-22 11:25:32 +08:00
procfs4.c Make each source file more consistent 2021-07-22 11:25:32 +08:00
sched.c Make each source file more consistent 2021-07-22 11:25:32 +08:00
sleep.c Improve the compatibility with kernel version < 5.6 2021-07-22 07:17:31 +08:00
start.c Enforce the customized style for example code 2021-07-22 06:58:13 +08:00
stop.c Enforce the customized style for example code 2021-07-22 06:58:13 +08:00
syscall.c Reduce header inclusion 2021-07-22 10:31:24 +08:00