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selinux: do not check open perm on ftruncate call 

Use the ATTR_FILE attribute to distinguish between truncate()
and ftruncate() system calls. The two other cases where
do_truncate is called with a filp (and therefore ATTR_FILE is set)
are for coredump files and for open(O_TRUNC). In both of those cases
the open permission has already been checked during file open and
therefore does not need to be repeated.

Commit 95dbf73931 ("SELinux: check OPEN on truncate calls")
fixed a major issue where domains were allowed to truncate files
without the open permission. However, it introduced a new bug where
a domain with the write permission can no longer ftruncate files
without the open permission, even when they receive an already open
file.

Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <pmoore@redhat.com>
This commit is contained in:
Jeff Vander Stoep 2015-10-21 17:44:25 -04:00 committed by Paul Moore
parent 2a35d196c1
commit 44d37ad360
1 changed files with 2 additions and 1 deletions
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3
security/selinux/hooks.c
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@ -2946,7 +2946,8 @@ static int selinux_inode_setattr(struct dentry *dentry, struct iattr *iattr)
ATTR_ATIME_SET | ATTR_MTIME_SET | ATTR_TIMES_SET))
return dentry_has_perm(cred, dentry, FILE__SETATTR);
if (selinux_policycap_openperm && (ia_valid & ATTR_SIZE))
if (selinux_policycap_openperm && (ia_valid & ATTR_SIZE)
&& !(ia_valid & ATTR_FILE))
av |= FILE__OPEN;
return dentry_has_perm(cred, dentry, av);