[PATCH] binfmt_misc: fix false -ENOEXEC when coupled with other binaryhandlers

[Pavel Emelyanov]

In case the binfmt_misc binary handler is registered *before* the
e.g. script one (when for example being compiled as a module) the
following situation may occur:

1. user launches a script, whose interpreter is a misc binary;
2. the load_misc_binary sets the misc_bang and returns -ENOEVEC,
   since the binary is a script;
3. the load_script_binary loads one and calls for search_binary_hander
   to run the interpreter;
4. the load_misc_binary is called again, but refuses to load the
   binary due to misc_bang bit set.

The fix is to move the misc_bang setting lower - prior to the actual
call to the search_binary_handler.

Caused by the commit 3a2e7f47 (binfmt_misc.c: avoid potential kernel 
stack overflow)

Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxx>
Reported-by: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Tested-by: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>

---

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 7562053..8d7e88e 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -120,8 +120,6 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 	if (bprm->misc_bang)
 		goto _ret;
 
-	bprm->misc_bang = 1;
-
 	/* to keep locking time low, we copy the interpreter string */
 	read_lock(&entries_lock);
 	fmt = check_file(bprm);
@@ -199,6 +197,8 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 	if (retval < 0)
 		goto _error;
 
+	bprm->misc_bang = 1;
+
 	retval = search_binary_handler (bprm, regs);
 	if (retval < 0)
 		goto _error;
--
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