alpha: binfmt_aout fix

This fixes the problem introduced by commit 3bfacef412 (get rid of
special-casing the /sbin/loader on alpha): osf/1 ecoff binary segfaults
when binfmt_aout built as module.  That happens because aout binary
handler gets on the top of the binfmt list due to late registration, and
kernel attempts to execute the binary without preparatory work that must
be done by binfmt_loader.

Fixed by changing the registration order of the default binfmt handlers
using list_add_tail() and introducing insert_binfmt() function which
places new handler on the top of the binfmt list.  This might be generally
useful for installing arch-specific frontends for default handlers or just
for overriding them.

Signed-off-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Richard Henderson <rth@twiddle.net
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 23 insertions, 6 deletions

diff --git a/arch/alpha/kernel/Makefile b/arch/alpha/kernel/Makefile
index a427538252f8..7739a62440a7 100644
--- a/arch/alpha/kernel/Makefile
+++ b/arch/alpha/kernel/Makefile
@@ -8,7 +8,7 @@ EXTRA_CFLAGS	:= -Werror -Wno-sign-compare
 
 obj-y    := entry.o traps.o process.o init_task.o osf_sys.o irq.o \
             irq_alpha.o signal.o setup.o ptrace.o time.o \
-            alpha_ksyms.o systbls.o err_common.o io.o binfmt_loader.o
+            alpha_ksyms.o systbls.o err_common.o io.o
 
 obj-$(CONFIG_VGA_HOSE)  += console.o
 obj-$(CONFIG_SMP)       += smp.o
@@ -43,6 +43,10 @@ else
 # Misc support
 obj-$(CONFIG_ALPHA_SRM)         += srmcons.o
 
+ifdef CONFIG_BINFMT_AOUT
+obj-y   += binfmt_loader.o
+endif
+
 # Core logic support
 obj-$(CONFIG_ALPHA_APECS)       += core_apecs.o
 obj-$(CONFIG_ALPHA_CIA)         += core_cia.o
diff --git a/arch/alpha/kernel/binfmt_loader.c b/arch/alpha/kernel/binfmt_loader.c
index 4a0af906b00a..3fcfad410130 100644
--- a/arch/alpha/kernel/binfmt_loader.c
+++ b/arch/alpha/kernel/binfmt_loader.c
@@ -46,6 +46,6 @@ static struct linux_binfmt loader_format = {
 
 static int __init init_loader_binfmt(void)
 {
-        return register_binfmt(&loader_format);
+        return insert_binfmt(&loader_format);
 }
 arch_initcall(init_loader_binfmt);
diff --git a/fs/exec.c b/fs/exec.c
index a3a8ce83940f..639177b0eeac 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -69,17 +69,18 @@ int suid_dumpable = 0;
 static LIST_HEAD(formats);
 static DEFINE_RWLOCK(binfmt_lock);
 
-int register_binfmt(struct linux_binfmt * fmt)
+int __register_binfmt(struct linux_binfmt * fmt, int insert)
 {
         if (!fmt)
                 return -EINVAL;
         write_lock(&binfmt_lock);
-        list_add(&fmt->lh, &formats);
+        insert ? list_add(&fmt->lh, &formats) :
+                 list_add_tail(&fmt->lh, &formats);
         write_unlock(&binfmt_lock);
         return 0;       
 }
 
-EXPORT_SYMBOL(register_binfmt);
+EXPORT_SYMBOL(__register_binfmt);
 
 void unregister_binfmt(struct linux_binfmt * fmt)
 {
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 6638b8148de7..61ee18c1bdb4 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -82,7 +82,19 @@ struct linux_binfmt {
         int hasvdso;
 };
 
-extern int register_binfmt(struct linux_binfmt *);
+extern int __register_binfmt(struct linux_binfmt *fmt, int insert);
+
+/* Registration of default binfmt handlers */
+static inline int register_binfmt(struct linux_binfmt *fmt)
+{
+        return __register_binfmt(fmt, 0);
+}
+/* Same as above, but adds a new binfmt at the top of the list */
+static inline int insert_binfmt(struct linux_binfmt *fmt)
+{
+        return __register_binfmt(fmt, 1);
+}
+
 extern void unregister_binfmt(struct linux_binfmt *);
 
 extern int prepare_binprm(struct linux_binprm *);