[ SRU Justification ][GROOVY][HIRSUTE][IMPISH]
== Impact ==
The ubuntu-host driver lacks procfs lseek ops and lseeking on the procfs esm-token file will jump to a NULL address causing the following splat:
942.470568] BUG: kernel NULL pointer dereference, address: 0000000000000000
[ 942.471157] #PF: supervisor instruction fetch in kernel mode
[ 942.471724] #PF: error_code(0x0010) - not-present page
[ 942.472297] PGD 0 P4D 0
[ 942.472867] Oops: 0010 [#1] SMP PTI
[ 942.473435] CPU: 2 PID: 5661 Comm: stress-ng Not tainted 5.13.0-9-generic #9
[ 942.474012] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
[ 942.474599] RIP: 0010:0x0
[ 942.475194] Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
[ 942.475792] RSP: 0018:ffffaacf80ff7eb8 EFLAGS: 00010246
[ 942.476383] RAX: 0000000000000000 RBX: ffff9eaa8a175240 RCX: 0000000000000001
[ 942.476986] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff9eaa838d5800
[ 942.477600] RBP: ffffaacf80ff7ed0 R08: 0000000000004000 R09: 0000000000000004
[ 942.478203] R10: 0000000000000002 R11: 0000000000000000 R12: 0000000000000000
[ 942.478800] R13: 0000000000000000 R14: ffffffffffffffea R15: ffff9eaa838d5800
[ 942.479399] FS: 00007f998d487f00(0000) GS:ffff9eaaffc80000(0000) knlGS:0000000000000000
[ 942.480006] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 942.480607] CR2: ffffffffffffffd6 CR3: 000000010a774002 CR4: 0000000000370ee0
[ 942.481219] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 942.481855] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 942.482458] Call Trace:
[ 942.483052] proc_reg_llseek+0x4e/0x80
[ 942.483646] ? __fdget_pos+0x43/0x50
[ 942.484234] ksys_lseek+0x84/0xc0
[ 942.484815] __x64_sys_lseek+0x1a/0x20
[ 942.485412] do_syscall_64+0x61/0xb0
[ 942.485966] ? asm_exc_page_fault+0x8/0x30
[ 942.486476] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 942.486994] RIP: 0033:0x7f998d5c1cdb
[ 942.487512] Code: ff ff c3 0f 1f 40 00 48 8b 15 89 81 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb ba 0f 1f 00 f3 0f 1e fa b8 08 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 05 c3 0f 1f 40 00 48 8b 15 59 81 0d 00 f7 d8
[ 942.488593] RSP: 002b:00007ffdf61c5328 EFLAGS: 00000246 ORIG_RAX: 0000000000000008
[ 942.489148] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f998d5c1cdb
[ 942.489710] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
[ 942.490252] RBP: 0000000000000004 R08: 000001785e4740dd R09: 0000562dbebb9e50
[ 942.490801] R10: 00007ffdf61c5300 R11: 0000000000000246 R12: 00007ffdf61c63f0
[ 942.491354] R13: 00007ffdf61c53f0 R14: 0000000000000003 R15: 00000000000001e9
== Fix ==
Add the default_llseek ops:
diff --git a/ubuntu/ubuntu-host/ubuntu-host.c b/ubuntu/ubuntu-host/ubuntu-host.c
index 1abd402..a4c0636 100644
--- a/ubuntu/ubuntu-host/ubuntu-host.c
+++ b/ubuntu/ubuntu-host/ubuntu-host.c
@@ -38,6 +38,8 @@ static ssize_t esm_token_write(struct file *f, const char __user *buf,
static const struct proc_ops esm_token_fops = {
.proc_read = esm_token_read,
.proc_write = esm_token_write,
+ .proc_lseek = default_llseek,
+
};
== Test plan ==
modrobe ubuntu-host
stress-ng --procfs 0 -t 60
without the fix we hit the splat. With the fix it's OK.
== Where problems could occur ==
This one liner adds the missing proc_lseek op. It is hard to see where it can cause a regression since it affects the driver no other way. I doubt any code is relying on the current semantics of lseek not working.
This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-
If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.
See https:/