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Allow recursion in binfmt_script and binfmt_misc

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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>
This commit is contained in:
Kirill A. Shutemov 2008-10-15 22:02:39 -07:00 committed by Linus Torvalds
parent 53112488be
commit bf2a9a3963
4 changed files with 8 additions and 5 deletions
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2
fs/binfmt_em86.c
View file

@ -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->recursion_depth++; /* Well, the bang-shell is implicit... */
allow_write_access(bprm->file);
fput(bprm->file);
bprm->file = NULL;

4
fs/binfmt_misc.c
View file

@ -117,7 +117,7 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
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_binprm *bprm, struct pt_regs *regs)
if (retval < 0)
goto _error;
bprm->misc_bang = 1;
bprm->recursion_depth++;
retval = search_binary_handler (bprm, regs);
if (retval < 0)

5
fs/binfmt_script.c
View file

@ -22,14 +22,15 @@ 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->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;

2
include/linux/binfmts.h
View file

@ -39,6 +39,7 @@ struct linux_binprm{
#ifdef __alpha__
unsigned int taso:1;
#endif
unsigned int recursion_depth;
struct file * file;
int e_uid, e_gid;
kernel_cap_t cap_post_exec_permitted;
@ -61,6 +62,7 @@ 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