On Fri, 11 Jan 2019 07:01:13 +0100 Andrea Righi righi.andrea@gmail.com wrote:

It is possible to trigger a NULL pointer dereference by writing an incorrectly formatted string to krpobe_events (trying to create a kretprobe omitting the symbol).

Example:

echo "r:event_1 " >> /sys/kernel/debug/tracing/kprobe_events

That triggers this:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 #PF error: [normal kernel read fault] PGD 0 P4D 0 Oops: 0000 [#1] SMP PTI CPU: 6 PID: 1757 Comm: bash Not tainted 5.0.0-rc1+ #125 Hardware name: Dell Inc. XPS 13 9370/0F6P3V, BIOS 1.5.1 08/09/2018 RIP: 0010:kstrtoull+0x2/0x20 Code: 28 00 00 00 75 17 48 83 c4 18 5b 41 5c 5d c3 b8 ea ff ff ff eb e1 b8 de ff ff ff eb da e8 d6 36 bb ff 66 0f 1f 44 00 00 31 c0 <80> 3f 2b 55 48 89 e5 0f 94 c0 48 01 c7 e8 5c ff ff ff 5d c3 66 2e RSP: 0018:ffffb5d482e57cb8 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 0000000000000001 RCX: ffffffff82b12720 RDX: ffffb5d482e57cf8 RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffffb5d482e57d70 R08: ffffa0c05e5a7080 R09: ffffa0c05e003980 R10: 0000000000000000 R11: 0000000040000000 R12: ffffa0c04fe87b08 R13: 0000000000000001 R14: 000000000000000b R15: ffffa0c058d749e1 FS: 00007f137c7f7740(0000) GS:ffffa0c05e580000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 0000000497d46004 CR4: 00000000003606e0 Call Trace: ? trace_kprobe_create+0xb6/0x840 ? _cond_resched+0x19/0x40 ? _cond_resched+0x19/0x40 ? __kmalloc+0x62/0x210 ? argv_split+0x8f/0x140 ? trace_kprobe_create+0x840/0x840 ? trace_kprobe_create+0x840/0x840 create_or_delete_trace_kprobe+0x11/0x30 trace_run_command+0x50/0x90 trace_parse_run_command+0xc1/0x160 probes_write+0x10/0x20 __vfs_write+0x3a/0x1b0 ? apparmor_file_permission+0x1a/0x20 ? security_file_permission+0x31/0xf0 ? _cond_resched+0x19/0x40 vfs_write+0xb1/0x1a0 ksys_write+0x55/0xc0 __x64_sys_write+0x1a/0x20 do_syscall_64+0x5a/0x120 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fix by doing the proper argument checks in trace_kprobe_create().

Thank you Andrea!

Acked-by: Masami Hiramatsu mhiramat@kernel.org

Link: https://lore.kernel.org/lkml/20190111095108.b79a2ee026185cbd62365977@kernel.... Fixes: 6212dd29683e ("tracing/kprobes: Use dyn_event framework for kprobe events") Cc: stable@vger.kernel.org Signed-off-by: Andrea Righi righi.andrea@gmail.com Signed-off-by: Masami Hiramatsu mhiramat@kernel.org

---

v2: argument check refactoring

kernel/trace/trace_kprobe.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c index 5c19b8c41c7e..d5fb09ebba8b 100644 --- a/kernel/trace/trace_kprobe.c +++ b/kernel/trace/trace_kprobe.c @@ -607,11 +607,17 @@ static int trace_kprobe_create(int argc, const char *argv[]) char buf[MAX_EVENT_NAME_LEN]; unsigned int flags = TPARG_FL_KERNEL;

• /* argc must be >= 1 */
• if (argv[0][0] == 'r') {

• switch (argv[0][0]) {
• case 'r': is_return = true; flags |= TPARG_FL_RETURN;

• } else if (argv[0][0] != 'p' || argc < 2)

• break;
  

• case 'p':

• break;
  

• default:

• return -ECANCELED;
  

• }
• if (argc < 2) return -ECANCELED;

event = strchr(&argv[0][1], ':'); -- 2.17.1