signal: Introduce COMPAT_SIGMINSTKSZ for use in compat_sys_sigaltstack

[ 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@arndb.de>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Oleg Nesterov <oleg@redhat.com>
Reported-by: Steve McIntyre <steve.mcintyre@arm.com>
Tested-by: Steve McIntyre <93sam@debian.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/compat.h b/include/linux/compat.h
index c68acc47da57b6a7bef7b8ef84a9c897d4b83ce6..47041c7fed28b7e15acfcd0c60c2b4edeb0b9922 100644 (file)
--- 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 8d8a940422a8e0d7758a46fecff34b26782e1787..41a5dd2df27d01db4c7c9ed73305dd812429b4d8 100644 (file)
--- 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);
        /* 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 (ret >= 0 && uoss_ptr)  {
                compat_stack_t old;
                memset(&old, 0, sizeof(old));