On Fri, 11 Jan 2019 07:01:13 +0100 Andrea Righi <righi.andrea@xxxxxxxxx> 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@xxxxxxxxxx> > > Link: https://lore.kernel.org/lkml/20190111095108.b79a2ee026185cbd62365977@xxxxxxxxxx > Fixes: 6212dd29683e ("tracing/kprobes: Use dyn_event framework for kprobe events") > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Andrea Righi <righi.andrea@xxxxxxxxx> > Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx> > --- > 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 > -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
