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SubjectRe: [PATCH v2] tracing/kprobes: fix NULL pointer dereference in trace_kprobe_create()
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.org
> 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
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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