[PATCH] ipcs: Avoid shmall overflows

[PATCH] ipcs: Avoid shmall overflows

[Vasilis Liaskovitis]

Avoid computing the number of bytes in shmall, by only
computing the number of Kbytes. This improves some
overflows, e.g.

$ echo "4503599627370496" > /proc/sys/kernel/shmall
$ ipcs -l | grep 'max total shared memory'
Before:
max total shared memory (kbytes) = 18014398509481980
After:
max total shared memory (kbytes) = 18014398509481984

$ echo "99993599627370500" > /proc/sys/kernel/shmall
99993599627370500
$ ipcs -l | grep 'max total shared memory'
Before:
max total shared memory (kbytes) = 18014398509481980
After:
max total shared memory (kbytes) = 399974398509482000

Signed-off-by: Vasilis Liaskovitis <vliaskovitis@suse.com>
---
 sys-utils/ipcs.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/sys-utils/ipcs.c b/sys-utils/ipcs.c
index fc6fba4a6..544a3adcc 100644
--- a/sys-utils/ipcs.c
+++ b/sys-utils/ipcs.c
@@ -216,13 +216,9 @@ static void do_shm (char format, int unit)
                ipc_print_size(unit == IPC_UNIT_DEFAULT ? IPC_UNIT_KB :
unit,
                               _("max seg size"), lim.shmmax, "\n", 0);

-               tmp = (uint64_t) lim.shmall * pgsz;
-               /* overflow handling, at least we don't print
ridiculous small values */
-               if (lim.shmall != 0 && tmp / lim.shmall != pgsz) {
-                       tmp = UINT64_MAX - (UINT64_MAX % pgsz);
-               }
-               ipc_print_size(unit == IPC_UNIT_DEFAULT ? IPC_UNIT_KB :
unit,
-                              _("max total shared memory"), tmp, "\n",
0);
+               ipc_print_size(IPC_UNIT_DEFAULT,
+                              _("max total shared memory (kbytes)"),
(pgsz / 1024) *
+                              (uint64_t) lim.shmall, "\n", 0);
                ipc_print_size(unit == IPC_UNIT_DEFAULT ?
IPC_UNIT_BYTES : unit,
                               _("min seg size"), lim.shmmin, "\n", 0);
                return;
--
2.28.0

Re: [PATCH] ipcs: Avoid shmall overflows

[Karel Zak]

On Wed, Dec 16, 2020 at 03:54:29PM +0100, Vasilis Liaskovitis wrote:
> Avoid computing the number of bytes in shmall, by only
> computing the number of Kbytes. This improves some
> overflows, e.g.
> 
> $ echo "4503599627370496" > /proc/sys/kernel/shmall
> $ ipcs -l | grep 'max total shared memory'
> Before:
> max total shared memory (kbytes) = 18014398509481980
> After:
> max total shared memory (kbytes) = 18014398509481984
> 
> $ echo "99993599627370500" > /proc/sys/kernel/shmall
> 99993599627370500
> $ ipcs -l | grep 'max total shared memory'
> Before:
> max total shared memory (kbytes) = 18014398509481980
> After:
> max total shared memory (kbytes) = 399974398509482000
> 
> Signed-off-by: Vasilis Liaskovitis <vliaskovitis@suse.com>
> ---
>  sys-utils/ipcs.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/sys-utils/ipcs.c b/sys-utils/ipcs.c
> index fc6fba4a6..544a3adcc 100644
> --- a/sys-utils/ipcs.c
> +++ b/sys-utils/ipcs.c
> @@ -216,13 +216,9 @@ static void do_shm (char format, int unit)
>                 ipc_print_size(unit == IPC_UNIT_DEFAULT ? IPC_UNIT_KB :
> unit,
>                                _("max seg size"), lim.shmmax, "\n", 0);
> 
> -               tmp = (uint64_t) lim.shmall * pgsz;
> -               /* overflow handling, at least we don't print
> ridiculous small values */
> -               if (lim.shmall != 0 && tmp / lim.shmall != pgsz) {
> -                       tmp = UINT64_MAX - (UINT64_MAX % pgsz);
> -               }
> -               ipc_print_size(unit == IPC_UNIT_DEFAULT ? IPC_UNIT_KB :
> unit,
> -                              _("max total shared memory"), tmp, "\n",
> 0);
> +               ipc_print_size(IPC_UNIT_DEFAULT,
> +                              _("max total shared memory (kbytes)"),
> (pgsz / 1024) *
> +                              (uint64_t) lim.shmall, "\n", 0);

It means that --bytes and --human command line options will be 
ignored for shmall ... it would be probably better to use

 if (unit == IPC_UNIT_KB || units == IPC_UNIT_DEFAULT)
    ipc_print_size(IPC_UNIT_KB, ("max total shared memory"), lim.shmall, "\n", 0); 
 else {
   tmp = (uint64_t) lim.shmall * pgsz;
   /* overflow handling, at least we don't print ridiculous small values */ 
   if (lim.shmall != 0 && tmp / lim.shmall != pgsz)
       tmp = UINT64_MAX - (UINT64_MAX % pgsz);
   ipc_print_size(unit, _("max total shared memory"), tmp, "\n", 0);
 }

 Right? If yes, update the patch, please.

   Karel
    

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com