broken __kernel_mode_t affecting some big endian archs

Submitted by Rich Felker on June 15, 2018, 2:01 a.m.

Details

Message ID 20180615020154.GN1392@brightrain.aerifal.cx
State New
Series "broken __kernel_mode_t affecting some big endian archs"
Headers show

Commit Message

Rich Felker June 15, 2018, 2:01 a.m.
On Thu, Jun 14, 2018 at 10:00:23PM -0400, Rich Felker wrote:
> On Wed, Jun 13, 2018 at 08:54:42PM -0400, Rich Felker wrote:
> > It's been semi-known for a long time (I say semi-, because nobody's
> > had the setup to test most of them well, or at least nobody I'm
> > communicating with regularly) that some archs are failing libc-test
> > sysvipc tests. I think I've tracked down the root cause.
> > 
> > Linux defined __kernel_mode_t as short on some old archs, and used it
> > in place of mode_t in the ipc_perm structure. The field is padded out
> > to 32 bits, so on little endian archs it's no problem for us to just
> > (as we do) ignore the incorrect type and declare the structure with
> > mode_t, as POSIX requires. However on big-endian archs, the padding is
> > on the wrong side and this trick doesn't work.
> > 
> > On MIPS we fixed a similar issue in struct stat, where dev_t was
> > incorrectly padded, with a fixup in syscall_arch.h. However this time
> > a large number of archs are affected, and patching them all up
> > individually seems nasty.
> > 
> > My leaning is to have syscall_arch.h expose a macro indicating the
> > bug, and have msgctl, semctl, and shmctl each do the fixup if it's
> > set.
> > 
> > FWIW the affected archs seem to be (only in big endian variants):
> > - ARM
> > - M68k (in-progress port)
> > - Microblaze
> > - SH
> > - Sparc (future port)
> > 
> > Thoughts?
> 
> Here's a draft of the fix, just for shmctl and not including the
> SHM_STAT or SHM_STAT_ALL operations.

And again with a fix so it doesn't break build on non-broken archs...

Rich

Patch hide | download patch | download mbox

diff --git a/src/ipc/shmctl.c b/src/ipc/shmctl.c
index e2879f2..9d723d9 100644
--- a/src/ipc/shmctl.c
+++ b/src/ipc/shmctl.c
@@ -4,9 +4,23 @@ 
 
 int shmctl(int id, int cmd, struct shmid_ds *buf)
 {
+#ifdef SYSCALL_IPC_BROKEN_MODE
+	struct shmid_ds tmp;
+	if (cmd == IPC_SET) {
+		tmp = *buf;
+		tmp.shm_perm.mode *= 0x10000U;
+		buf = &tmp;
+	}
+#endif
 #ifdef SYS_shmctl
-	return syscall(SYS_shmctl, id, cmd | IPC_64, buf);
+	int r = __syscall(SYS_shmctl, id, cmd | IPC_64, buf);
 #else
-	return syscall(SYS_ipc, IPCOP_shmctl, id, cmd | IPC_64, 0, buf, 0);
+	int r = __syscall(SYS_ipc, IPCOP_shmctl, id, cmd | IPC_64, 0, buf, 0);
+#endif
+#ifdef SYSCALL_IPC_BROKEN_MODE
+	if (r >= 0 && cmd == IPC_STAT) {
+		buf->shm_perm.mode >>= 16;
+	}
 #endif
+	return __syscall_ret(r);
 }

Comments

Szabolcs Nagy June 16, 2018, 12:14 a.m.
* Rich Felker <dalias@libc.org> [2018-06-14 22:01:54 -0400]:
> diff --git a/src/ipc/shmctl.c b/src/ipc/shmctl.c
> index e2879f2..9d723d9 100644
> --- a/src/ipc/shmctl.c
> +++ b/src/ipc/shmctl.c
> @@ -4,9 +4,23 @@
>  
>  int shmctl(int id, int cmd, struct shmid_ds *buf)
>  {
> +#ifdef SYSCALL_IPC_BROKEN_MODE
> +	struct shmid_ds tmp;
> +	if (cmd == IPC_SET) {
> +		tmp = *buf;
> +		tmp.shm_perm.mode *= 0x10000U;
> +		buf = &tmp;
> +	}
> +#endif
>  #ifdef SYS_shmctl
> -	return syscall(SYS_shmctl, id, cmd | IPC_64, buf);
> +	int r = __syscall(SYS_shmctl, id, cmd | IPC_64, buf);
>  #else
> -	return syscall(SYS_ipc, IPCOP_shmctl, id, cmd | IPC_64, 0, buf, 0);
> +	int r = __syscall(SYS_ipc, IPCOP_shmctl, id, cmd | IPC_64, 0, buf, 0);
> +#endif
> +#ifdef SYSCALL_IPC_BROKEN_MODE
> +	if (r >= 0 && cmd == IPC_STAT) {
> +		buf->shm_perm.mode >>= 16;
> +	}
>  #endif
> +	return __syscall_ret(r);
>  }

ugly but looks ok to me.
i don't think there is a clean solution on the broken targets.