On Wed, Jul 25, 2018 at 02:45:11PM +0100, Will Deacon wrote: > The sigaltstack(2) system call fails with -ENOMEM if the new alternative > signal stack is found to be smaller than SIGMINSTKSZ. On architectures > such as arm64, where the native value for SIGMINSTKSZ is larger than > the compat value, this can result in an unexpected error being reported > to a compat task. See, for example: > > https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=904385 > > This patch fixes the problem by extending do_sigaltstack to take the > minimum signal stack size as an additional parameter, allowing the > native and compat system call entry code to pass in their respective > values. COMPAT_SIGMINSTKSZ is just defined as SIGMINSTKSZ if it has not > been defined by the architecture. > > Cc: Arnd Bergmann <a...@arndb.de> > Cc: Dominik Brodowski <li...@dominikbrodowski.net> > Cc: "Eric W. Biederman" <ebied...@xmission.com> > Cc: Andrew Morton <a...@linux-foundation.org> > Cc: Al Viro <v...@zeniv.linux.org.uk> > Cc: Oleg Nesterov <o...@redhat.com> > Reported-by: Steve McIntyre <steve.mcint...@arm.com> > Signed-off-by: Will Deacon <will.dea...@arm.com> > --- > include/linux/compat.h | 3 +++ > kernel/signal.c | 14 +++++++++----- > 2 files changed, 12 insertions(+), 5 deletions(-) > > diff --git a/include/linux/compat.h b/include/linux/compat.h > index c68acc47da57..47041c7fed28 100644 > --- a/include/linux/compat.h > +++ b/include/linux/compat.h > @@ -103,6 +103,9 @@ typedef struct compat_sigaltstack { > compat_size_t ss_size; > } compat_stack_t; > #endif > +#ifndef COMPAT_MINSIGSTKSZ > +#define COMPAT_MINSIGSTKSZ MINSIGSTKSZ > +#endif > > #define compat_jiffies_to_clock_t(x) \ > (((unsigned long)(x) * COMPAT_USER_HZ) / HZ) > diff --git a/kernel/signal.c b/kernel/signal.c > index 8d8a940422a8..41a5dd2df27d 100644 > --- a/kernel/signal.c > +++ b/kernel/signal.c > @@ -3417,7 +3417,8 @@ int do_sigaction(int sig, struct k_sigaction *act, > struct k_sigaction *oact) > } > > static int > -do_sigaltstack (const stack_t *ss, stack_t *oss, unsigned long sp) > +do_sigaltstack (const stack_t *ss, stack_t *oss, unsigned long sp, > + size_t min_ss_size) > { > struct task_struct *t = current; > > @@ -3447,7 +3448,7 @@ do_sigaltstack (const stack_t *ss, stack_t *oss, > unsigned long sp) > ss_size = 0; > ss_sp = NULL; > } else { > - if (unlikely(ss_size < MINSIGSTKSZ)) > + if (unlikely(ss_size < min_ss_size)) > return -ENOMEM; > } > > @@ -3465,7 +3466,8 @@ SYSCALL_DEFINE2(sigaltstack,const stack_t __user *,uss, > stack_t __user *,uoss) > if (uss && copy_from_user(&new, uss, sizeof(stack_t))) > return -EFAULT; > err = do_sigaltstack(uss ? &new : NULL, uoss ? &old : NULL, > - current_user_stack_pointer()); > + current_user_stack_pointer(), > + MINSIGSTKSZ); > if (!err && uoss && copy_to_user(uoss, &old, sizeof(stack_t))) > err = -EFAULT; > return err; > @@ -3476,7 +3478,8 @@ int restore_altstack(const stack_t __user *uss) > stack_t new; > if (copy_from_user(&new, uss, sizeof(stack_t))) > return -EFAULT; > - (void)do_sigaltstack(&new, NULL, current_user_stack_pointer()); > + (void)do_sigaltstack(&new, NULL, current_user_stack_pointer(), > + MINSIGSTKSZ);
Why can't this fail? If this fails here we silently go wrong, but... > /* squash all but EFAULT for now */ > return 0; > } > @@ -3510,7 +3513,8 @@ static int do_compat_sigaltstack(const compat_stack_t > __user *uss_ptr, > uss.ss_size = uss32.ss_size; > } > ret = do_sigaltstack(uss_ptr ? &uss : NULL, &uoss, > - compat_user_stack_pointer()); > + compat_user_stack_pointer(), > + COMPAT_MINSIGSTKSZ); If this fails on arm64, we seem to SEGV (see compat_sys_rt_sigreturn()). This patch doesn't introduce this inconsistency, this might be a good opportunity to clean it up. Cheers ---Dave
