[3.19.y-ckt stable] Patch "ring-buffer: Use long for nr_pages to avoid overflow failures" has been added to the 3.19.y-ckt tree

Kamal Mostafa kamal at canonical.com
Wed Jul 6 21:00:52 UTC 2016


This is a note to let you know that I have just added a patch titled

    ring-buffer: Use long for nr_pages to avoid overflow failures

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt23.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 54ff99a0cf957e3397a120d0733418634a50b163 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Red Hat)" <rostedt at goodmis.org>
Date: Thu, 12 May 2016 11:01:24 -0400
Subject: ring-buffer: Use long for nr_pages to avoid overflow failures

commit 9b94a8fba501f38368aef6ac1b30e7335252a220 upstream.

The size variable to change the ring buffer in ftrace is a long. The
nr_pages used to update the ring buffer based on the size is int. On 64 bit
machines this can cause an overflow problem.

For example, the following will cause the ring buffer to crash:

 # cd /sys/kernel/debug/tracing
 # echo 10 > buffer_size_kb
 # echo 8556384240 > buffer_size_kb

Then you get the warning of:

 WARNING: CPU: 1 PID: 318 at kernel/trace/ring_buffer.c:1527 rb_update_pages+0x22f/0x260

Which is:

  RB_WARN_ON(cpu_buffer, nr_removed);

Note each ring buffer page holds 4080 bytes.

This is because:

 1) 10 causes the ring buffer to have 3 pages.
    (10kb requires 3 * 4080 pages to hold)

 2) (2^31 / 2^10  + 1) * 4080 = 8556384240
    The value written into buffer_size_kb is shifted by 10 and then passed
    to ring_buffer_resize(). 8556384240 * 2^10 = 8761737461760

 3) The size passed to ring_buffer_resize() is then divided by BUF_PAGE_SIZE
    which is 4080. 8761737461760 / 4080 = 2147484672

 4) nr_pages is subtracted from the current nr_pages (3) and we get:
    2147484669. This value is saved in a signed integer nr_pages_to_update

 5) 2147484669 is greater than 2^31 but smaller than 2^32, a signed int
    turns into the value of -2147482627

 6) As the value is a negative number, in update_pages_handler() it is
    negated and passed to rb_remove_pages() and 2147482627 pages will
    be removed, which is much larger than 3 and it causes the warning
    because not all the pages asked to be removed were removed.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=118001

Fixes: 7a8e76a3829f1 ("tracing: unified trace buffer")
Reported-by: Hao Qin <QEver.cn at gmail.com>
Signed-off-by: Steven Rostedt <rostedt at goodmis.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 kernel/trace/ring_buffer.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 3dd43de..8533ec9 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -463,7 +463,7 @@ struct ring_buffer_per_cpu {
 	raw_spinlock_t			reader_lock;	/* serialize readers */
 	arch_spinlock_t			lock;
 	struct lock_class_key		lock_key;
-	unsigned int			nr_pages;
+	unsigned long			nr_pages;
 	struct list_head		*pages;
 	struct buffer_page		*head_page;	/* read from head */
 	struct buffer_page		*tail_page;	/* write to tail */
@@ -483,7 +483,7 @@ struct ring_buffer_per_cpu {
 	u64				write_stamp;
 	u64				read_stamp;
 	/* ring buffer pages to update, > 0 to add, < 0 to remove */
-	int				nr_pages_to_update;
+	long				nr_pages_to_update;
 	struct list_head		new_pages; /* new pages to add */
 	struct work_struct		update_pages_work;
 	struct completion		update_done;
@@ -1162,10 +1162,10 @@ static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
 	return 0;
 }

-static int __rb_allocate_pages(int nr_pages, struct list_head *pages, int cpu)
+static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu)
 {
-	int i;
 	struct buffer_page *bpage, *tmp;
+	long i;

 	for (i = 0; i < nr_pages; i++) {
 		struct page *page;
@@ -1202,7 +1202,7 @@ free_pages:
 }

 static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
-			     unsigned nr_pages)
+			     unsigned long nr_pages)
 {
 	LIST_HEAD(pages);

@@ -1227,7 +1227,7 @@ static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 }

 static struct ring_buffer_per_cpu *
-rb_allocate_cpu_buffer(struct ring_buffer *buffer, int nr_pages, int cpu)
+rb_allocate_cpu_buffer(struct ring_buffer *buffer, long nr_pages, int cpu)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
 	struct buffer_page *bpage;
@@ -1327,8 +1327,9 @@ struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
 					struct lock_class_key *key)
 {
 	struct ring_buffer *buffer;
+	long nr_pages;
 	int bsize;
-	int cpu, nr_pages;
+	int cpu;

 	/* keep it in its own cache line */
 	buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
@@ -1454,12 +1455,12 @@ static inline unsigned long rb_page_write(struct buffer_page *bpage)
 }

 static int
-rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned int nr_pages)
+rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned long nr_pages)
 {
 	struct list_head *tail_page, *to_remove, *next_page;
 	struct buffer_page *to_remove_page, *tmp_iter_page;
 	struct buffer_page *last_page, *first_page;
-	unsigned int nr_removed;
+	unsigned long nr_removed;
 	unsigned long head_bit;
 	int page_entries;

@@ -1676,7 +1677,7 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
 			int cpu_id)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
-	unsigned nr_pages;
+	unsigned long nr_pages;
 	int cpu, err = 0;

 	/*
@@ -4650,8 +4651,9 @@ static int rb_cpu_notify(struct notifier_block *self,
 	struct ring_buffer *buffer =
 		container_of(self, struct ring_buffer, cpu_notify);
 	long cpu = (long)hcpu;
-	int cpu_i, nr_pages_same;
-	unsigned int nr_pages;
+	long nr_pages_same;
+	int cpu_i;
+	unsigned long nr_pages;

 	switch (action) {
 	case CPU_UP_PREPARE:
--
2.7.4





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