Re: [syzbot] [mm?] INFO: rcu detected stall in kcov_ioctl (2)

[Uladzislau Rezki]

On Mon, Jul 29, 2024 at 02:31:12PM -0700, Andrew Morton wrote:
> On Mon, 29 Jul 2024 08:34:33 -0700 syzbot <syzbot+ff2407cef5068e202465@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> 
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    3a7e02c040b1 minmax: avoid overly complicated constant exp..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=132e32bd980000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=381b8eb3d35e3ad9
> > dashboard link: https://syzkaller.appspot.com/bug?extid=ff2407cef5068e202465
> > compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> > 
> > Unfortunately, I don't have any reproducer for this issue yet.
> > 
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/198814da854c/disk-3a7e02c0.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/868e99275bc0/vmlinux-3a7e02c0.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/ce63033f3708/bzImage-3a7e02c0.xz
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+ff2407cef5068e202465@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> Thanks.  Possibly kcov_ioctl(KCOV_INIT_TRACE) was passed a crazily huge
> size.  Perhaps some more realistic checking should be applied there?
> 
> Also, vmalloc() shouldn't be doing this even if asked to allocate a
> crazily huge size.
> 
<snip>
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index bc21d821d506..450c6b10a357 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3783,7 +3783,7 @@ void *__vmalloc_node_range_noprof(unsigned long size, unsigned long align,
 	if (WARN_ON_ONCE(!size))
 		return NULL;
 
-	if ((size >> PAGE_SHIFT) > totalram_pages()) {
+	if ((size >> PAGE_SHIFT) > totalram_pages() || size > INT32_MAX) {
 		warn_alloc(gfp_mask, NULL,
 			"vmalloc error: size %lu, exceeds total pages",
 			real_size);
<snip>

We can limit it to ~2GB or add a special threshold which will control
the maximum allocation size.

Any thoughts?

--
Uladzislau Rezki