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Subject[patch 78/83] Allow recursion in binfmt_script and binfmt_misc
2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Kirill A. Shutemov <kirill@shutemov.name>

commit bf2a9a39639b8b51377905397a5005f444e9a892 upstream.

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.

This patch introduces field 'recursion_depth' into struct linux_binprm to
track recursion level in binfmt_misc and binfmt_script. If recursion
level more then BINPRM_MAX_RECURSION it generates -ENOEXEC.

[akpm@linux-foundation.org: make linux_binprm.recursion_depth a uint]
Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/binfmt_em86.c | 2 +-
fs/binfmt_misc.c | 4 ++--
fs/binfmt_script.c | 5 +++--
include/linux/binfmts.h | 2 ++
4 files changed, 8 insertions(+), 5 deletions(-)
--- a/fs/binfmt_em86.c
+++ b/fs/binfmt_em86.c
@@ -43,7 +43,7 @@ static int load_em86(struct linux_binprm
return -ENOEXEC;
}

- bprm->sh_bang = 1; /* Well, the bang-shell is implicit... */
+ bprm->recursion_depth++; /* Well, the bang-shell is implicit... */
allow_write_access(bprm->file);
fput(bprm->file);
bprm->file = NULL;
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -117,7 +117,7 @@ static int load_misc_binary(struct linux
goto _ret;

retval = -ENOEXEC;
- if (bprm->misc_bang)
+ if (bprm->recursion_depth > BINPRM_MAX_RECURSION)
goto _ret;

/* to keep locking time low, we copy the interpreter string */
@@ -197,7 +197,7 @@ static int load_misc_binary(struct linux
if (retval < 0)
goto _error;

- bprm->misc_bang = 1;
+ bprm->recursion_depth++;

retval = search_binary_handler (bprm, regs);
if (retval < 0)
--- a/fs/binfmt_script.c
+++ b/fs/binfmt_script.c
@@ -22,14 +22,15 @@ static int load_script(struct linux_binp
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->recursion_depth > BINPRM_MAX_RECURSION))
return -ENOEXEC;
/*
* This section does the #! interpretation.
* Sorta complicated, but hopefully it will work. -TYT
*/

- bprm->sh_bang = 1;
+ bprm->recursion_depth++;
allow_write_access(bprm->file);
fput(bprm->file);
bprm->file = NULL;
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -36,6 +36,7 @@ struct linux_binprm{
unsigned long p; /* current top of mem */
unsigned int sh_bang:1,
misc_bang:1;
+ unsigned int recursion_depth;
struct file * file;
int e_uid, e_gid;
kernel_cap_t cap_post_exec_permitted;
@@ -58,6 +59,7 @@ struct linux_binprm{
#define BINPRM_FLAGS_EXECFD_BIT 1
#define BINPRM_FLAGS_EXECFD (1 << BINPRM_FLAGS_EXECFD_BIT)

+#define BINPRM_MAX_RECURSION 4

/*
* This structure defines the functions that are used to load the binary formats that


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