Messages in this thread Patch in this message | | | Date | Mon, 3 Jul 2023 12:18:23 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] trace: fix null pointer dereference in tracing_err_log_open() |
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On Mon, 03 Jul 2023 17:52:37 +0200 Mateusz Stachyra <m.stachyra@samsung.com> wrote:
> >From d6ef949d29b884dd77fe5e628dc71318de08868c Mon Sep 17 00:00:00 2001 > From: Mateusz Stachyra <m.stachyra@samsung.com> > Date: Mon, 3 Jul 2023 17:48:40 +0200 > Subject: [PATCH] trace: fix null pointer dereference in tracing_err_log_open() > > Fix an issue in function 'tracing_err_log_open'. > The function doesn't call 'seq_open' if file is opened only with > write permissions, which results in 'file->private_data' being left at null. > If we then use 'lseek' on that opened file, 'seq_lseek' dereferences > 'file->private_data' in 'mutex_lock(&m->lock)', resulting in a Kernel panic. > Writing to this node requires root privilages, therefore this bug > has very little security impact. > > Tracefs node: /sys/kernel/tracing/error_log >
Nice catch, but I recommend a different solution.
> Example Kernel panic: > > Unable to handle kernel NULL pointer dereference at virtual address 0000000000000038 > Call trace: > mutex_lock+0x30/0x110 > seq_lseek+0x34/0xb8 > __arm64_sys_lseek+0x6c/0xb8 > invoke_syscall+0x58/0x13c > el0_svc_common+0xc4/0x10c > do_el0_svc+0x24/0x98 > el0_svc+0x24/0x88 > el0t_64_sync_handler+0x84/0xe4 > el0t_64_sync+0x1b4/0x1b8 > Code: d503201f aa0803e0 aa1f03e1 aa0103e9 (c8e97d02) > ---[ end trace 561d1b49c12cf8a5 ]--- > Kernel panic - not syncing: Oops: Fatal exception > > Signed-off-by: Mateusz Stachyra <m.stachyra@samsung.com> > --- > kernel/trace/trace.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 5d2c5678b..bfa8e2d01 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -8097,8 +8097,16 @@ static int tracing_err_log_open(struct inode *inode, struct file *file) > return ret; > > /* If this file was opened for write, then erase contents */ > - if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) > + if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) { > clear_tracing_err_log(tr); > + ret = seq_open(file, &tracing_err_log_seq_ops); > + if (!ret) { > + struct seq_file *m = file->private_data; > + m->private = tr; > + } else { > + trace_array_put(tr); > + } > + } > > if (file->f_mode & FMODE_READ) { > ret = seq_open(file, &tracing_err_log_seq_ops); > > base-commit: 1ef6663a587ba3e57dc5065a477db1c64481eedd
I believe this can be better fixed by:
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 64a4dde073ef..999b7c73e324 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8135,7 +8135,7 @@ static const struct file_operations tracing_err_log_fops = { .open = tracing_err_log_open, .write = tracing_err_log_write, .read = seq_read, - .llseek = seq_lseek, + .llseek = tracing_lseek, .release = tracing_err_log_release, };
as that tracing_lseek() is for this exact scenario. Care to send a v2?
Thanks,
-- Steve
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