[GIT PULL] tracing/kprobes: Fix NULL pointer dereference in trace_kprobe_create()

[Steven Rostedt]

Linus,

Andrea Righi fixed a NULL pointer dereference in trace_kprobe_create()

It is possible to trigger a NULL pointer dereference by writing an
incorrectly formatted string to the krpobe_events file.


Please pull the latest trace-v5.0-rc1 tree, which can be found at:


  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
trace-v5.0-rc1

Tag SHA1: f29b31ca77f34e8fd81b06f3c47850fefba37a4d
Head SHA1: 8b05a3a7503c2a982c9c462eae96cfbd59506783


Andrea Righi (1):
      tracing/kprobes: Fix NULL pointer dereference in trace_kprobe_create()

----
 kernel/trace/trace_kprobe.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)
---------------------------
commit 8b05a3a7503c2a982c9c462eae96cfbd59506783
Author: Andrea Righi <righi.andrea@xxxxxxxxx>
Date:   Fri Jan 11 07:01:13 2019 +0100

    tracing/kprobes: Fix NULL pointer dereference in trace_kprobe_create()
    
    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().
    
    Cc: Ingo Molnar <mingo@xxxxxxxxxx>
    Link: https://lore.kernel.org/lkml/20190111095108.b79a2ee026185cbd62365977@xxxxxxxxxx
    Link: 20190111060113.GA22841@xps-13">http://lkml.kernel.org/r/20190111060113.GA22841@xps-13
    Fixes: 6212dd29683e ("tracing/kprobes: Use dyn_event framework for kprobe events")
    Acked-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
    Signed-off-by: Andrea Righi <righi.andrea@xxxxxxxxx>
    Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
    Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>

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], ':');