Re: Request to cherry-pick 20401d1058f3f841f35a594ac2fc1293710e55b9 to v5.10 and v5.4

[Manfred Spraul]

Hi,

On 9/2/22 16:27, Greg Kroah-Hartman wrote:
> On Fri, Sep 02, 2022 at 01:59:11PM +0000, Varsha Teratipally wrote:
> > Hi all,
> >
> > Commit 20401d1058f3f841f35a594ac2fc1293710e55b9("ipc: replace costly
> > bailout check in sysvipc_find_ipc()" fixes a high cve and optimizes the
> > costly loop by adding a checkpoint, which I think might be a good
> > candidate for the stable branches
> What do you mean by "high cve"?
>
> And that feels like it's an artificial benchmark fixup, what real
> workload benefits from this change?

Standard ipcs end up parsing /proc/sysvipc/*, thus there are real users 
where the performance of /proc/sysvsem/* matters.

But:

The performance of the function was bad since 2007, i.e. why is is now 
urgent? I do not see a bug that must be fixed.

Initial patch:

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/ipc/util.c?id=7ca7e564e049d8b350ec9d958ff25eaa24226352

(core issue: The code needs to find the next entry in an idr. And 
instead of using idr_get_next(), it uses idr_find() in a for(;;id++) loop.)

<<<

[manfred@localhost Input]$ rpm -qf /usr/bin/ipcs
util-linux-core-2.38-1.fc36.x86_64


[manfred@localhost Input]$ strace -e openat /usr/bin/ipcs
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/usr/lib/locale/en_US.UTF-8/LC_TIME", 
O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/locale/en_US.utf8/LC_TIME", 
O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/usr/lib64/gconv/gconv-modules.cache", O_RDONLY) = 3

openat(AT_FDCWD, 
"/usr/share/locale/en_US.UTF-8/LC_MESSAGES/util-linux.mo", O_RDONLY) = 
-1 ENOENT (No such file or directory)
openat(AT_FDCWD, 
"/usr/share/locale/en_US.utf8/LC_MESSAGES/util-linux.mo", O_RDONLY) = -1 
ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en_US/LC_MESSAGES/util-linux.mo", 
O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en.UTF-8/LC_MESSAGES/util-linux.mo", 
O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en.utf8/LC_MESSAGES/util-linux.mo", 
O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en/LC_MESSAGES/util-linux.mo", 
O_RDONLY) = -1 ENOENT (No such file or directory)
------ Message Queues --------
key        msqid      owner      perms      used-bytes messages
openat(AT_FDCWD, "/proc/sysvipc/msg", O_RDONLY) = 3

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch status
openat(AT_FDCWD, "/proc/sysvipc/shm", O_RDONLY) = 3
openat(AT_FDCWD, "/etc/nsswitch.conf", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
0x00000000 18         manfred    600        524288     2 dest
openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
0x5125004a 19         manfred    600        3208 1

------ Semaphore Arrays --------
key        semid      owner      perms      nsems
openat(AT_FDCWD, "/proc/sysvipc/sem", O_RDONLY) = 3
openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
0x51250047 0          manfred    600        1
openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
0x51250049 2          manfred    600        1

>>>