glibc: the x86 mem[r]chr changes cause random segfaults

[Manuel Lauss]

On Wed, Jun 8, 2022 at 9:59 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> On Wed, Jun 8, 2022 at 12:54 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> > On Wed, Jun 8, 2022 at 12:06 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> > >
> > > On Wed, Jun 8, 2022 at 11:57 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> > > >
> > > > On Wed, Jun 8, 2022 at 11:22 AM Manuel Lauss via Libc-alpha
> > > > <libc-alpha@sourceware.org> wrote:
> > > > >
> > > > > Hi Noah,
> > > > >
> > > > > One of your recent x86 mem[r]chr patches to glibc causes random segfaults in
> > > > > gcc;  I haven't nailed it down to a single patch yet, but a glibc built
> > > > > up to commit 0218463dd8265ed937622f88ac68c7d984fe0cfc (all your
> > > > > commits from 07th June reverted) works just fine.
> > > > > For me it's very easy to reproduce, just rebuild glibc.
> > > > >
> > > > > The backtraces all look like this (sorry, no debug symbols for gcc):
> > > > > #0  0x00007fdd9df1d36a in __GI___libc_free (mem=0x672f7ffcc7137ff0) at
> > > > > malloc.c:3368
> > > > > warning: Source file is more recent than executable.
> > > > > 3368      if (chunk_is_mmapped (p))                       /* release
> > > > > mmapped memory. */
> > > > > (gdb) bt
> > > > > #0  0x00007fdd9df1d36a in __GI___libc_free (mem=0x672f7ffcc7137ff0) at
> > > > > malloc.c:3368
> > > > > #1  0x00007fdd9debe3e0 in scratch_buffer_free (buffer=0x7ffcc7137fe0)
> > > > > at ../include/scratch_buffer.h:86
> > > > > #2  realpath_stk (name=<optimized out>, resolved=<optimized out>,
> > > > > rname_buf=rname_buf@entry=0x7ffcc7137fe0) at canonicalize.c:423
> > > > > #3  0x00007fdd9debeaff in __GI___realpath (name=<optimized out>,
> > > > > resolved=<optimized out>) at canonicalize.c:449
> > > >
> > > > I suspect that rawmemchr isn't properly handled.
> > > >
> > >
> > > Correct. The new code changes how pointers were aligned in the page cross
> > > case and didn't adjust rawmemchr accordingly.
> > >
> >
> > Made bugzilla and posted fix there. Testing right now:
> > https://sourceware.org/bugzilla/show_bug.cgi?id=29234

Hello,

The patch fixes the issue for me.

Thank you!
     Manuel