Re: [PATCH] exec: Fix a deadlock in ptrace

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Sun, Mar 1, 2020 at 12:27 PM Bernd Edlinger
<bernd.edlinger@xxxxxxxxxx> wrote:
> The proposed solution is to have a second mutex that is
> used in mm_access, so it is allowed to continue while the
> dying threads are not yet terminated.

Just for context: When I proposed something similar back in 2016,
https://lore.kernel.org/linux-fsdevel/20161102181806.GB1112@xxxxxxxxxx/
was the resulting discussion thread. At least back then, I looked
through the various existing users of cred_guard_mutex, and the only
places that couldn't be converted to the new second mutex were
PTRACE_ATTACH and SECCOMP_FILTER_FLAG_TSYNC.


The ideal solution would IMO be something like this: Decide what the
new task's credentials should be *before* reaching de_thread(),
install them into a second cred* on the task (together with the new
dumpability), drop the cred_guard_mutex, and let ptrace_may_access()
check against both. After that, some further restructuring might even
allow the cred_guard_mutex to not be held across all of the VFS
operations that happen early on in execve, which may block
indefinitely. But that would be pretty complicated, so I think your
proposed solution makes sense for now, given that nobody has managed
to implement anything better in the last few years.



[Index of Archives]     [Kernel Newbies]     [Security]     [Netfilter]     [Bugtraq]     [Linux FS]     [Yosemite Forum]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Video 4 Linux]     [Device Mapper]     [Linux Resources]

  Powered by Linux