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Message-ID: <47D95834.8020706@openvz.org>
Date: Thu, 13 Mar 2008 19:37:08 +0300
From: Pavel Emelyanov <xemul@...nvz.org>
To: Andrew Morton <akpm@...ux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH] Avoid potential kernel stack overflow in binfmt_misc.c
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: Pavel Emelyanov <xemul@...nvz.org>
---
diff --git a/fs/binfmt_em86.c b/fs/binfmt_em86.c
index f95ae97..f9c88d0 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++; /* 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;
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index b53c7e5..d7d1b00 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -116,6 +116,12 @@ 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);
diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c
index ab33939..9e3963f 100644
--- a/fs/binfmt_script.c
+++ b/fs/binfmt_script.c
@@ -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;
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 1dd7567..b512e48 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -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;
--
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