Hi all,
While fuzzing with trinity inside a KVM tools guest running the latest -next
kernel, I've stumbled on the following:
[ 2052.444910] WARNING: CPU: 3 PID: 26525 at mm/page_alloc.c:2513 __alloc_pages_slowpat
h+0x6a/0x801()
[ 2052.447575] Modules linked in:
[ 2052.448438] CPU: 3 PID: 26525 Comm: trinity-c3 Tainted: G W 3.14.0-next-2
0140407-sasha-00023-gd35b0d6 #382
[ 2052.452147] 0000000000000009 ffff88010f485af8 ffffffff9d52ee51 0000000000005d20
[ 2052.454425] 0000000000000000 ffff88010f485b38 ffffffff9a15a2dc 000000174802a016
[ 2052.456676] 00000000001040d0 0000000000000000 0000000000000002 0000000000000000
[ 2052.458851] Call Trace:
[ 2052.459587] dump_stack (lib/dump_stack.c:52)
[ 2052.461211] warn_slowpath_common (kernel/panic.c:419)
[ 2052.462914] warn_slowpath_null (kernel/panic.c:454)
[ 2052.464512] __alloc_pages_slowpath (mm/page_alloc.c:2513 (discriminator 3))
[ 2052.466160] ? get_page_from_freelist (mm/page_alloc.c:1939)
[ 2052.468020] ? sched_clock_local (kernel/sched/clock.c:213)
[ 2052.469633] ? get_parent_ip (kernel/sched/core.c:2471)
[ 2052.471329] __alloc_pages_nodemask (mm/page_alloc.c:2766)
[ 2052.473084] alloc_pages_current (mm/mempolicy.c:2131)
[ 2052.474688] ? __get_free_pages (mm/page_alloc.c:2803)
[ 2052.476273] ? __free_pages_ok (arch/x86/include/asm/paravirt.h:809 (discriminator 2) mm/page_alloc.c:766 (discriminator 2))
[ 2052.477980] __get_free_pages (mm/page_alloc.c:2803)
[ 2052.481082] kmalloc_order_trace (include/linux/slab.h:379 mm/slab_common.c:525)
[ 2052.483193] __kmalloc (include/linux/slab.h:396 mm/slub.c:3303)
[ 2052.485417] ? kfree (mm/slub.c:3395)
[ 2052.486337] traverse (fs/seq_file.c:141)
[ 2052.487289] seq_read (fs/seq_file.c:179 (discriminator 1))
[ 2052.488161] vfs_read (fs/read_write.c:408)
[ 2052.489001] SyS_pread64 (include/linux/file.h:38 fs/read_write.c:557 fs/read_write.c:544)
[ 2052.489959] tracesys (arch/x86/kernel/entry_64.S:749)
It seems that when we attempt to read huge chunks of data from a seq file
there would be no check for the size being read, leading to the kernel
attempting to allocate huge chunks of data internally.
As far as I remember, there was a PAGE_SIZE limitation on those, but I'm
not certain about that. Could someone please confirm it?
Thanks,
Sasha
On Tue, Apr 08, 2014 at 10:45:31AM -0400, Sasha Levin wrote:
> It seems that when we attempt to read huge chunks of data from a seq file
> there would be no check for the size being read, leading to the kernel
> attempting to allocate huge chunks of data internally.
>
> As far as I remember, there was a PAGE_SIZE limitation on those, but I'm
> not certain about that. Could someone please confirm it?
I've had this diff sitting around for a while to figure out which
seq_file we're talking about. I think Al wrote it, I forget..
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 1d641bb108d2..e3ca909c8fea 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -82,7 +82,7 @@ int seq_open(struct file *file, const struct seq_operations *op)
}
EXPORT_SYMBOL(seq_open);
-static int traverse(struct seq_file *m, loff_t offset)
+static int traverse(struct file *file, struct seq_file *m, loff_t offset)
{
loff_t pos = 0, index;
int error = 0;
@@ -137,6 +137,13 @@ Eoverflow:
m->op->stop(m, p);
kfree(m->buf);
m->count = 0;
+ if ((m->size <<= 1) >= (PAGE_SIZE << 4)) {
+ printk(KERN_ERR "traverse on %s. Size: %ld\n",
+ file->f_path.dentry->d_name.name,
+ (unsigned long) (m->size));
+ m->buf = NULL;
+ return -ENOMEM;
+ }
m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
return !m->buf ? -ENOMEM : -EAGAIN;
}
@@ -176,7 +183,7 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
/* Don't assume *ppos is where we left it */
if (unlikely(*ppos != m->read_pos)) {
- while ((err = traverse(m, *ppos)) == -EAGAIN)
+ while ((err = traverse(file, m, *ppos)) == -EAGAIN)
;
if (err) {
/* With prejudice... */
@@ -192,6 +199,14 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
/* grab buffer if we didn't have one */
if (!m->buf) {
+ if ((m->size <<= 1) >= (PAGE_SIZE << 4)) {
+ printk(KERN_ERR "seq_read on %s. Size: %ld\n",
+ file->f_path.dentry->d_name.name,
+ (unsigned long) (m->size));
+ m->buf = NULL;
+ goto Enomem;;
+ }
+
m->buf = kmalloc(m->size = PAGE_SIZE, GFP_KERNEL);
if (!m->buf)
goto Enomem;
@@ -234,6 +249,15 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
m->op->stop(m, p);
kfree(m->buf);
m->count = 0;
+
+ if ((m->size <<= 1) >= (PAGE_SIZE << 4)) {
+ printk(KERN_ERR "seq_read on %s. Size: %ld\n",
+ file->f_path.dentry->d_name.name,
+ (unsigned long) (m->size));
+ m->buf = NULL;
+ goto Enomem;;
+ }
+
m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
if (!m->buf)
goto Enomem;
@@ -316,7 +340,7 @@ loff_t seq_lseek(struct file *file, loff_t offset, int whence)
break;
retval = offset;
if (offset != m->read_pos) {
- while ((retval = traverse(m, offset)) == -EAGAIN)
+ while ((retval = traverse(file, m, offset)) == -EAGAIN)
;
if (retval) {
/* with extreme prejudice... */
On 04/08/2014 10:49 AM, Dave Jones wrote:
> On Tue, Apr 08, 2014 at 10:45:31AM -0400, Sasha Levin wrote:
>
> > It seems that when we attempt to read huge chunks of data from a seq file
> > there would be no check for the size being read, leading to the kernel
> > attempting to allocate huge chunks of data internally.
> >
> > As far as I remember, there was a PAGE_SIZE limitation on those, but I'm
> > not certain about that. Could someone please confirm it?
>
> I've had this diff sitting around for a while to figure out which
> seq_file we're talking about. I think Al wrote it, I forget..
I'll add it in.
I didn't realize it was a problem with a specific file, I thought it was
an issue with seq files in general.
Thanks,
Sasha