From: Will Deacon <will.deacon@xxxxxxx> [ 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 <arnd@xxxxxxxx> Cc: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx> Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Reported-by: Steve McIntyre <steve.mcintyre@xxxxxxx> Tested-by: Steve McIntyre <93sam@xxxxxxxxxx> Signed-off-by: Will Deacon <will.deacon@xxxxxxx> Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- 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 3e838a828459..23909d12f729 100644 --- 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) diff --git a/kernel/signal.c b/kernel/signal.c index 4439ba9dc5d9..b74acbec9876 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -3215,7 +3215,8 @@ 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; @@ -3245,7 +3246,7 @@ 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; } @@ -3263,7 +3264,8 @@ 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; @@ -3274,7 +3276,8 @@ 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); /* 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)); -- 2.17.1
