[PATCH 04/10] proc: fix PAGE_SIZE limit of /proc/$PID/cmdline

[PATCH 04/10] proc: fix PAGE_SIZE limit of /proc/$PID/cmdline

[Alexey Dobriyan]

Convert /proc/$PID/cmdline to seq_file interface.

XXX

This one must be buggy.

seq_file buffer is adjustable, so userspace can execute itself
with huge command line (which can be arbitrarily long now), then read 1 byte.

Voila, whole command line now is in kmalloced/vmalloced memory.

Imposing limit is trivial but equally lame to current PAGE_SIZE limit.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 fs/proc/base.c |   16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -200,9 +200,17 @@ static int proc_root_link(struct dentry *dentry, struct path *path)
 	return result;
 }
 
-static int proc_pid_cmdline(struct task_struct *task, char *buffer)
+static int proc_pid_cmdline(struct seq_file *m, struct pid_namespace *ns,
+			    struct pid *pid, struct task_struct *task)
 {
-	return get_cmdline(task, buffer, PAGE_SIZE);
+	/*
+	 * Rely on struct seq_operations::show() being called once
+	 * per internal buffer allocation. See single_open(), traverse().
+	 *
+	 * Rely on internal buffer autoexpansion if it was entirely filled.
+	 */
+	m->count += get_cmdline(task, m->buf, m->size);
+	return 0;
 }
 
 static int proc_pid_auxv(struct seq_file *m, struct pid_namespace *ns,
@@ -2567,7 +2575,7 @@ static const struct pid_entry tgid_base_stuff[] = {
 #ifdef CONFIG_HAVE_ARCH_TRACEHOOK
 	ONE("syscall",    S_IRUSR, proc_pid_syscall),
 #endif
-	INF("cmdline",    S_IRUGO, proc_pid_cmdline),
+	ONE("cmdline",    S_IRUGO, proc_pid_cmdline),
 	ONE("stat",       S_IRUGO, proc_tgid_stat),
 	ONE("statm",      S_IRUGO, proc_pid_statm),
 	REG("maps",       S_IRUGO, proc_pid_maps_operations),
@@ -2903,7 +2911,7 @@ static const struct pid_entry tid_base_stuff[] = {
 #ifdef CONFIG_HAVE_ARCH_TRACEHOOK
 	ONE("syscall",   S_IRUSR, proc_pid_syscall),
 #endif
-	INF("cmdline",   S_IRUGO, proc_pid_cmdline),
+	ONE("cmdline",   S_IRUGO, proc_pid_cmdline),
 	ONE("stat",      S_IRUGO, proc_tid_stat),
 	ONE("statm",     S_IRUGO, proc_pid_statm),
 	REG("maps",      S_IRUGO, proc_tid_maps_operations),

Re: [PATCH 04/10] proc: fix PAGE_SIZE limit of /proc/$PID/cmdline

[Andrew Morton]

On Thu, 17 Jul 2014 00:32:47 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:

> Convert /proc/$PID/cmdline to seq_file interface.
> 
> XXX

Unsure what XXX signifies.

> This one must be buggy.
> 
> seq_file buffer is adjustable, so userspace can execute itself
> with huge command line (which can be arbitrarily long now), then read 1 byte.
> 
> Voila, whole command line now is in kmalloced/vmalloced memory.
> 
> Imposing limit is trivial but equally lame to current PAGE_SIZE limit.

Confused. Why send the patch if you don't like it?

Why not go ahead and impose the PAGE_SIZE limit?

Re: [PATCH 04/10] proc: fix PAGE_SIZE limit of /proc/$PID/cmdline

[Alexey Dobriyan]

On Thu, Jul 17, 2014 at 03:53:46PM -0700, Andrew Morton wrote:
> On Thu, 17 Jul 2014 00:32:47 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:
> 
> > Convert /proc/$PID/cmdline to seq_file interface.
> > 
> > XXX
> 
> Unsure what XXX signifies.
> 
> > This one must be buggy.
> > 
> > seq_file buffer is adjustable, so userspace can execute itself
> > with huge command line (which can be arbitrarily long now), then read 1 byte.
> > 
> > Voila, whole command line now is in kmalloced/vmalloced memory.
> > 
> > Imposing limit is trivial but equally lame to current PAGE_SIZE limit.
> 
> Confused. Why send the patch if you don't like it?
> 
> Why not go ahead and impose the PAGE_SIZE limit?

I thought someone smarter than me would suggest what to do.

Please replace with v2.

[PATCH v2 04/10] proc: convert /proc/$PID/cmdline to seq_file interface

[Alexey Dobriyan]

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 fs/proc/base.c |   15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -200,9 +200,16 @@ static int proc_root_link(struct dentry *dentry, struct path *path)
 	return result;
 }
 
-static int proc_pid_cmdline(struct task_struct *task, char *buffer)
+static int proc_pid_cmdline(struct seq_file *m, struct pid_namespace *ns,
+			    struct pid *pid, struct task_struct *task)
 {
-	return get_cmdline(task, buffer, PAGE_SIZE);
+	/*
+	 * Rely on struct seq_operations::show() being called once
+	 * per internal buffer allocation. See single_open(), traverse().
+	 */
+	BUG_ON(m->size < PAGE_SIZE);
+	m->count += get_cmdline(task, m->buf, PAGE_SIZE);
+	return 0;
 }
 
 static int proc_pid_auxv(struct seq_file *m, struct pid_namespace *ns,
@@ -2567,7 +2574,7 @@ static const struct pid_entry tgid_base_stuff[] = {
 #ifdef CONFIG_HAVE_ARCH_TRACEHOOK
 	ONE("syscall",    S_IRUSR, proc_pid_syscall),
 #endif
-	INF("cmdline",    S_IRUGO, proc_pid_cmdline),
+	ONE("cmdline",    S_IRUGO, proc_pid_cmdline),
 	ONE("stat",       S_IRUGO, proc_tgid_stat),
 	ONE("statm",      S_IRUGO, proc_pid_statm),
 	REG("maps",       S_IRUGO, proc_pid_maps_operations),
@@ -2903,7 +2910,7 @@ static const struct pid_entry tid_base_stuff[] = {
 #ifdef CONFIG_HAVE_ARCH_TRACEHOOK
 	ONE("syscall",   S_IRUSR, proc_pid_syscall),
 #endif
-	INF("cmdline",   S_IRUGO, proc_pid_cmdline),
+	ONE("cmdline",   S_IRUGO, proc_pid_cmdline),
 	ONE("stat",      S_IRUGO, proc_tid_stat),
 	ONE("statm",     S_IRUGO, proc_pid_statm),
 	REG("maps",      S_IRUGO, proc_tid_maps_operations),