[linux-lvm] Frequent crashes when accessing dev_name(dev) on an empty list

[linux-lvm] Frequent crashes when accessing dev_name(dev) on an empty list

[Konstantin Kharlamov]

Hello! We encountered quite a few of sporadic crashes, which upon inspection turned out to be caused by dev->aliases list being empty.

One example of a fix (not tested):

--- a/lib/label/hints.c
+++ b/lib/label/hints.c
@@ -471,7 +471,8 @@ int validate_hints(struct cmd_context *cmd, struct dm_list
*hints)
    471         if (!(iter = dev_iter_create(NULL, 0)))
    472                 return 0;
    473         while ((dev = dev_iter_get(cmd, iter))) {
474    -                if (!(hint = _find_hint_name(hints, dev_name(dev))))
    474+                if (dm_list_empty(dev->aliases) ||
    475+                    !(hint = _find_hint_name(hints, dev_name(dev))))
475 476                         continue;
476 477
477 478                 /* The cmd hasn't needed this hint's dev so it's not
been scanned. */

So, what happened was that dev_name(dev) was extracting a `dev->aliases` element
, however `dev->aliases` was empty, thus the extracted element was a junk.

Although we encountered these crashes on an older 2.03.07 version, however the
patch applies to latest master as well, thus the bugs are still relevant, which
is odd. This makes me wondering, is this a known problem, could I possibly
overlooked something, for example that dev->aliases should never be empty, and
thus the fix just works around another problem? Any thoughts?

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Re: [linux-lvm] Frequent crashes when accessing dev_name(dev) on an empty list

[David Teigland]

On Mon, Feb 21, 2022 at 04:45:51PM +0300, Konstantin Kharlamov wrote:
> So, what happened was that dev_name(dev) was extracting a `dev->aliases` element
> , however `dev->aliases` was empty, thus the extracted element was a junk.
> 
> Although we encountered these crashes on an older 2.03.07 version, however the
> patch applies to latest master as well, thus the bugs are still relevant, which
> is odd. This makes me wondering, is this a known problem, could I possibly
> overlooked something, for example that dev->aliases should never be empty, and
> thus the fix just works around another problem? Any thoughts?

It's familiar, but I thought it was fixed.  I don't remember the details,
so we'll have to look at it again.  It's related to a device being removed
from the system while the command is running, which we need to add tests
for.

Dave

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Re: [linux-lvm] Frequent crashes when accessing dev_name(dev) on an empty list

[Konstantin Kharlamov]

On Mon, 2022-02-21 at 10:49 -0600, David Teigland wrote:
> On Mon, Feb 21, 2022 at 04:45:51PM +0300, Konstantin Kharlamov wrote:
> > So, what happened was that dev_name(dev) was extracting a `dev->aliases`
> > element
> > , however `dev->aliases` was empty, thus the extracted element was a junk.
> > 
> > Although we encountered these crashes on an older 2.03.07 version, however
> > the
> > patch applies to latest master as well, thus the bugs are still relevant,
> > which
> > is odd. This makes me wondering, is this a known problem, could I possibly
> > overlooked something, for example that dev->aliases should never be empty,
> > and
> > thus the fix just works around another problem? Any thoughts?
> 
> It's familiar, but I thought it was fixed.  I don't remember the details,
> so we'll have to look at it again.  It's related to a device being removed
> from the system while the command is running, which we need to add tests
> for.

Okay, thank you, so I guess the conclusion is that before anything else we need to reproduce it with the latest version.


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Re: [linux-lvm] Frequent crashes when accessing dev_name(dev) on an empty list

[Konstantin Kharlamov]

To close the topic: there was a discussion off-list, and a number of fixes were
merged. Some of them were tested by us as well (we backported them to older
LVM), and it's been more than a month since with no crashes. So the problem is
fixed.

On Mon, 2022-02-21 at 16:45 +0300, Konstantin Kharlamov wrote:
> Hello! We encountered quite a few of sporadic crashes, which upon inspection
> turned out to be caused by dev->aliases list being empty.
> 
> One example of a fix (not tested):
> 
> --- a/lib/label/hints.c
> +++ b/lib/label/hints.c
> @@ -471,7 +471,8 @@ int validate_hints(struct cmd_context *cmd, struct dm_list
> *hints)
>     471         if (!(iter = dev_iter_create(NULL, 0)))
>     472                 return 0;
>     473         while ((dev = dev_iter_get(cmd, iter))) {
> 474    -                if (!(hint = _find_hint_name(hints, dev_name(dev))))
>     474+                if (dm_list_empty(dev->aliases) ||
>     475+                    !(hint = _find_hint_name(hints, dev_name(dev))))
> 475 476                         continue;
> 476 477
> 477 478                 /* The cmd hasn't needed this hint's dev so it's not
> been scanned. */
> 
> So, what happened was that dev_name(dev) was extracting a `dev->aliases`
> element
> , however `dev->aliases` was empty, thus the extracted element was a junk.
> 
> Although we encountered these crashes on an older 2.03.07 version, however the
> patch applies to latest master as well, thus the bugs are still relevant,
> which
> is odd. This makes me wondering, is this a known problem, could I possibly
> overlooked something, for example that dev->aliases should never be empty, and
> thus the fix just works around another problem? Any thoughts?
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://listman.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
> 

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