4.14-stable review patch. If anyone has any objections, please let me know.
------------------ From: Will Deacon <[email protected]> [ Upstream commit 22839869f21ab3850fbbac9b425ccc4c0023926f ] 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 <[email protected]> Cc: Dominik Brodowski <[email protected]> Cc: "Eric W. Biederman" <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Al Viro <[email protected]> Cc: Oleg Nesterov <[email protected]> Reported-by: Steve McIntyre <[email protected]> Tested-by: Steve McIntyre <[email protected]> Signed-off-by: Will Deacon <[email protected]> Signed-off-by: Catalin Marinas <[email protected]> Signed-off-by: Sasha Levin <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- include/linux/compat.h | 3 +++ kernel/signal.c | 14 +++++++++----- 2 files changed, 12 insertions(+), 5 deletions(-) --- a/include/linux/compat.h +++ b/include/linux/compat.h @@ -68,6 +68,9 @@ 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) --- a/kernel/signal.c +++ b/kernel/signal.c @@ -3215,7 +3215,8 @@ int do_sigaction(int sig, struct k_sigac } 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; @@ -3245,7 +3246,7 @@ do_sigaltstack (const stack_t *ss, stack ss_size = 0; ss_sp = NULL; } else { - if (unlikely(ss_size < MINSIGSTKSZ)) + if (unlikely(ss_size < min_ss_size)) return -ENOMEM; } @@ -3263,7 +3264,8 @@ SYSCALL_DEFINE2(sigaltstack,const stack_ 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; @@ -3274,7 +3276,8 @@ int restore_altstack(const stack_t __use 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); /* squash all but EFAULT for now */ return 0; } @@ -3309,7 +3312,8 @@ COMPAT_SYSCALL_DEFINE2(sigaltstack, 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 (ret >= 0 && uoss_ptr) { compat_stack_t old; memset(&old, 0, sizeof(old));
