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Commit bf2a9a39 authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds
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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.

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: default avatarKirill A. Shutemov <kirill@shutemov.name>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 53112488

fs/binfmt_em86.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

fs/binfmt_misc.c

+2 −2
Original line number Diff line number Diff line
@@ -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)

fs/binfmt_script.c

+3 −2
Original line number Diff line number Diff line
@@ -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;

include/linux/binfmts.h

+2 −0
Original line number Diff line number Diff line
@@ -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