Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 3a2e7f47 authored by Pavel Emelyanov's avatar Pavel Emelyanov Committed by Linus Torvalds
Browse files

binfmt_misc.c: avoid potential kernel stack overflow 



This can be triggered with root help only, but...

Register the ":text:E::txt::/root/cat.txt:' rule in binfmt_misc (by root) and
try launching the cat.txt file (by anyone) :) The result is - the endless
recursion in the load_misc_binary -> open_exec -> load_misc_binary chain and
stack overflow.

There's a similar problem with binfmt_script, and there's a sh_bang memner on
linux_binprm structure to handle this, but simply raising this in binfmt_misc
may break some setups when the interpreter of some misc binaries is a script.

So the proposal is to turn sh_bang into a bit, add a new one (the misc_bang)
and raise it in load_misc_binary.  After this, even if we set up the misc ->
script -> misc loop for binfmts one of them will step on its own bang and
exit.

Signed-off-by: default avatarPavel Emelyanov <xemul@openvz.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent cbd9b67b

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++;	/* Well, the bang-shell is implicit... */

	bprm->sh_bang = 1;	/* Well, the bang-shell is implicit... */

	allow_write_access(bprm->file);

	fput(bprm->file);

	bprm->file = NULL;

fs/binfmt_misc.c

+6 −0
Original line number Diff line number Diff line
@@ -115,6 +115,12 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs) 
	if (!enabled)

		goto _ret;



	retval = -ENOEXEC;

	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);

fs/binfmt_script.c

+1 −1
Original line number Diff line number Diff line
@@ -29,7 +29,7 @@ static int load_script(struct linux_binprm *bprm,struct pt_regs *regs) 
	 * Sorta complicated, but hopefully it will work.  -TYT

	 */



	bprm->sh_bang++;

	bprm->sh_bang = 1;

	allow_write_access(bprm->file);

	fput(bprm->file);

	bprm->file = NULL;

include/linux/binfmts.h

+2 −1
Original line number Diff line number Diff line
@@ -34,7 +34,8 @@ struct linux_binprm{ 
#endif

	struct mm_struct *mm;

	unsigned long p; /* current top of mem */

	int sh_bang;

	unsigned int sh_bang:1,

		     misc_bang:1;

	struct file * file;

	int e_uid, e_gid;

	kernel_cap_t cap_inheritable, cap_permitted;