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Hao Qin reported an integer overflow possibility with signed and

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unsigned numbers in the ring-buffer code.
 
   https://bugzilla.kernel.org/show_bug.cgi?id=118001
 
 At first I did not think this was too much of an issue, because the
 overflow would be caught later when either too much data was allocated
 or it would trigger RB_WARN_ON() which shuts down the ring buffer.
 
 But looking closer into it, I found that the right settings could bypass
 the checks and crash the kernel. Luckily, this is only accessible
 by root.
 
 The first fix is to convert all the variables into long, such that
 we don't get into issues between 32 bit variables being assigned 64 bit
 ones. This fixes the RB_WARN_ON() triggering.
 
 The next fix is to get rid of a duplicate DIV_ROUND_UP() that when called
 twice with the right value, can cause a kernel crash.
 
 The first DIV_ROUND_UP() is to normalize the input and it is checked
 against the minimum allowable value. But then DIV_ROUND_UP() is called
 again, which can overflow due to the (a + b - 1)/b, logic. The first
 called upped the value, the second can overflow (with the +b part).
 
 The second call to DIV_ROUND_UP() came in via a second change a while ago
 and the code is cleaned up to remove it.
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Merge tag 'trace-fixes-v4.6-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing ring-buffer fixes from Steven Rostedt:
 "Hao Qin reported an integer overflow possibility with signed and
  unsigned numbers in the ring-buffer code.

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

  At first I did not think this was too much of an issue, because the
  overflow would be caught later when either too much data was allocated
  or it would trigger RB_WARN_ON() which shuts down the ring buffer.

  But looking closer into it, I found that the right settings could
  bypass the checks and crash the kernel.  Luckily, this is only
  accessible by root.

  The first fix is to convert all the variables into long, such that we
  don't get into issues between 32 bit variables being assigned 64 bit
  ones.  This fixes the RB_WARN_ON() triggering.

  The next fix is to get rid of a duplicate DIV_ROUND_UP() that when
  called twice with the right value, can cause a kernel crash.

  The first DIV_ROUND_UP() is to normalize the input and it is checked
  against the minimum allowable value.  But then DIV_ROUND_UP() is
  called again, which can overflow due to the (a + b - 1)/b, logic.  The
  first called upped the value, the second can overflow (with the +b
  part).

  The second call to DIV_ROUND_UP() came in via a second change a while
  ago and the code is cleaned up to remove it"

* tag 'trace-fixes-v4.6-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  ring-buffer: Prevent overflow of size in ring_buffer_resize()
  ring-buffer: Use long for nr_pages to avoid overflow failures
This commit is contained in:
Linus Torvalds 2016-05-17 09:42:58 -07:00
commit 2fe2edf85f
1 changed files with 18 additions and 17 deletions
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35
kernel/trace/ring_buffer.c
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@ -437,7 +437,7 @@ 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;
unsigned int current_context;
struct list_head *pages;
struct buffer_page *head_page; /* read from head */
@ -458,7 +458,7 @@ 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;
@ -1128,10 +1128,10 @@ 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;
@ -1168,7 +1168,7 @@ free_pages:
}
static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
unsigned nr_pages)
unsigned long nr_pages)
{
LIST_HEAD(pages);
@ -1193,7 +1193,7 @@ 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;
@ -1293,8 +1293,9 @@ 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()),
@ -1420,12 +1421,12 @@ 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;
@ -1642,7 +1643,7 @@ 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;
/*
@ -1656,14 +1657,13 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
!cpumask_test_cpu(cpu_id, buffer->cpumask))
return size;
size = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
size *= BUF_PAGE_SIZE;
nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
/* we need a minimum of two pages */
if (size < BUF_PAGE_SIZE * 2)
size = BUF_PAGE_SIZE * 2;
if (nr_pages < 2)
nr_pages = 2;
nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
size = nr_pages * BUF_PAGE_SIZE;
/*
* Don't succeed if resizing is disabled, as a reader might be
@ -4640,8 +4640,9 @@ 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: