Hi Finn,
On Sat, Aug 10, 2024 at 9:14 AM Finn Thain <fthain@xxxxxxxxxxxxxx> wrote:
Stan Johnson recently reported a failure from the 'dump' command:
DUMP: Date of this level 0 dump: Fri Aug 9 23:37:15 2024
DUMP: Dumping /dev/sda (an unlisted file system) to /dev/null
DUMP: Label: none
DUMP: Writing 10 Kilobyte records
DUMP: mapping (Pass I) [regular files]
DUMP: mapping (Pass II) [directories]
DUMP: estimated 3595695 blocks.
DUMP: Context save fork fails in parent 671
The dump program uses the clone syscall with the CLONE_IO flag, that is,
flags == 0x80000000. When that value is cast from long int to u64 by
m68k_clone(), it undergoes sign-extension. The new value includes
CLONE_INTO_CGROUP so the validation in cgroup_css_set_fork() fails and
the syscall returns -EBADFD.
Avoid sign-extension by adopting the idiom used in kernel/fork.c when
casting clone flags.
Cc: Stan Johnson <userm57@xxxxxxxxx>
Reported-by: Stan Johnson <userm57@xxxxxxxxx>
Closes: https://lists.debian.org/debian-68k/2024/08/msg00000.html
Fixes: 6aabc1facdb2 ("m68k: Implement copy_thread_tls()")
Signed-off-by: Finn Thain <fthain@xxxxxxxxxxxxxx>
Thanks for your patch!
--- a/arch/m68k/kernel/process.c
+++ b/arch/m68k/kernel/process.c
@@ -117,7 +117,7 @@ asmlinkage int m68k_clone(struct pt_regs *regs)
{
/* regs will be equal to current_pt_regs() */
struct kernel_clone_args args = {
- .flags = regs->d1 & ~CSIGNAL,
+ .flags = (lower_32_bits(regs->d1) & ~CSIGNAL),
While other architectures (nios2, sparc, generic code) do use
lower_32_bits() in similar code[*], IMHO this is misleading here, as
regs->d1 is never 64-bit. What you really want is to avoid the sign
extension in the promotion from signed 32-bit to unsigned 64-bit.
So I think a cast to u32 makes more sense?
.pidfd = (int __user *)regs->d3,
.child_tid = (int __user *)regs->d4,
.parent_tid = (int __user *)regs->d3,
[*] The shared sparc32/64 code uses lower_32_bits on unsigned long,
which is 64-bit on sparc64. Likewise for the generic code in kernel/fork.c.
The nios2 code is a bit moot, as clone_flags is already unsigned, and
unsigned long is always 32-bit on nios2.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
