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Message-ID: <406D69D2.10306@informatik.hu-berlin.de>
Date: Fri, 02 Apr 2004 15:25:38 +0200
From: Stefan Nordhausen <deletethis.nordhaus@informatik.hu-berlin.de>
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To: linux-kernel@vger.kernel.org
Subject: chown() not POSIX compliant in 2.2.* and 2.4.*
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Hi,
I noted that chown will not always take away the SGID bit from
nondirectories. Posix says the following about it (taken from [1]):
"If the path argument refers to a regular file, the set-user-ID
(S_ISUID) and set-group-ID (S_ISGID) bits of the file mode shall be
cleared upon successful return from chown(), unless the call is made by
process with appropriate privileges [=root], in which case it is
implementation defined whether those bits are altered."
As far as I can tell the 2.6.* kernel is Posix compliant as it will
always remove both SUID and SGID. 2.2.* and 2.4.* will _only_ remove the
SGID bit if the file is group executable. This is not Posix compliant
and it is also a potential security whole (as in my case). So I suggest
the attached patch against 2.4.26rc1. It will make chown always clear
the SGID bit, just like 2.6 does.
MfG
Stefan Nordhausen
[1] http://mail-index.netbsd.org/netbsd-bugs/1997/12/10/0003.html
--
Not only does god play dice. The dice are loaded.
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diff -Naur linux-2.4.26rc1/fs/open.c linux-2.4.26rc1_/fs/open.c
--- linux-2.4.26rc1/fs/open.c 2004-04-02 14:46:26.000000000 +0200
+++ linux-2.4.26rc1_/fs/open.c 2004-04-02 15:01:21.000000000 +0200
@@ -587,8 +587,10 @@
* 19981026 David C Niemi <niemi@tux.org>
*
* Removed the fsuid check (see the comment above) -- 19990830 SD.
+ *
+ * Always remove SGID bit to comply with POSIX.
*/
- if (((inode->i_mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP))
+ if (((inode->i_mode & S_ISGID) == S_ISGID)
&& !S_ISDIR(inode->i_mode))
{
newattrs.ia_mode &= ~S_ISGID;
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