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Message-ID: <20080902110648.GA5027@localhost.localdomain>
Date: Tue, 2 Sep 2008 14:06:52 +0300
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Pavel Emelyanov <xemul@...nvz.org>
Cc: Al Viro <viro@...iv.linux.org.uk>,
Richard Henderson <rth@...ddle.net>,
linux-kernel@...r.kernel.org
Subject: [PATCH] [RFC] Allow recursion in binfmt_script and binfmt_misc
binfmt_script and binfmt_misc disallow recursion to avoid stack overflow
using sh_bang and misc_bang. It causes problem in some cases:
$ echo '#!/bin/ls' > /tmp/t0
$ echo '#!/tmp/t0' > /tmp/t1
$ echo '#!/tmp/t1' > /tmp/t2
$ chmod +x /tmp/t*
$ /tmp/t2
zsh: exec format error: /tmp/t2
Similar problem with binfmt_misc.
I propose allow recursion, but limit its deep.
There is one more problem: on Alpha sh_bang used to remember if the
application is TASO. I have no experience with Alpha. Is it possible to
use separate flag in struct linux_binprm for it?
Signed-off-by: Kirill A. Shutemov <kirill@...temov.name>
diff --git a/fs/binfmt_em86.c b/fs/binfmt_em86.c
index f9c88d0..f95ae97 100644
--- a/fs/binfmt_em86.c
+++ b/fs/binfmt_em86.c
@@ -43,7 +43,7 @@ static int load_em86(struct linux_binprm *bprm,struct pt_regs *regs)
return -ENOEXEC;
}
- bprm->sh_bang = 1; /* Well, the bang-shell is implicit... */
+ bprm->sh_bang++; /* Well, the bang-shell is implicit... */
allow_write_access(bprm->file);
fput(bprm->file);
bprm->file = NULL;
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 8d7e88e..50c665f 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -43,6 +43,8 @@ enum {Enabled, Magic};
#define MISC_FMT_OPEN_BINARY (1<<30)
#define MISC_FMT_CREDENTIALS (1<<29)
+#define MISC_FMT_MAX_RECURSION 4
+
typedef struct {
struct list_head list;
unsigned long flags; /* type, status, etc. */
@@ -117,7 +119,7 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
goto _ret;
retval = -ENOEXEC;
- if (bprm->misc_bang)
+ if (bprm->misc_bang >= MISC_FMT_MAX_RECURSION)
goto _ret;
/* to keep locking time low, we copy the interpreter string */
@@ -197,7 +199,7 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
if (retval < 0)
goto _error;
- bprm->misc_bang = 1;
+ bprm->misc_bang++;
retval = search_binary_handler (bprm, regs);
if (retval < 0)
diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c
index 9e3963f..172c954 100644
--- a/fs/binfmt_script.c
+++ b/fs/binfmt_script.c
@@ -15,6 +15,8 @@
#include <linux/err.h>
#include <linux/fs.h>
+#define SCRIPT_FMT_MAX_RECURSION 4
+
static int load_script(struct linux_binprm *bprm,struct pt_regs *regs)
{
char *cp, *i_name, *i_arg;
@@ -22,14 +24,15 @@ static int load_script(struct linux_binprm *bprm,struct pt_regs *regs)
char interp[BINPRM_BUF_SIZE];
int retval;
- if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!') || (bprm->sh_bang))
+ if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!') ||
+ (bprm->sh_bang >= SCRIPT_FMT_MAX_RECURSION))
return -ENOEXEC;
/*
* This section does the #! interpretation.
* Sorta complicated, but hopefully it will work. -TYT
*/
- bprm->sh_bang = 1;
+ bprm->sh_bang++;
allow_write_access(bprm->file);
fput(bprm->file);
bprm->file = NULL;
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 826f623..1e21ff0 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -34,8 +34,8 @@ struct linux_binprm{
#endif
struct mm_struct *mm;
unsigned long p; /* current top of mem */
- unsigned int sh_bang:1,
- misc_bang:1;
+ unsigned char sh_bang;
+ unsigned char misc_bang;
struct file * file;
int e_uid, e_gid;
kernel_cap_t cap_post_exec_permitted;
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