Use access mode instead of open flags to determine needed permissions (CVE-2008-0001)

patch 974a9f0b47da74e28f68b9c8645c3786aa5ace1a in mainline

Way back when (in commit 834f2a4a1554dc5b2598038b3fe8703defcbe467, aka
"VFS: Allow the filesystem to return a full file pointer on open intent"
to be exact), Trond changed the open logic to keep track of the original
flags to a file open, in order to pass down the the intent of a dentry
lookup to the low-level filesystem.

However, when doing that reorganization, it changed the meaning of
namei_flags, and thus inadvertently changed the test of access mode for
directories (and RO filesystem) to use the wrong flag.  So fix those
test back to use access mode ("acc_mode") rather than the open flag
("flag").

Issue noticed by Bill Roman at Datalight.

Reported-and-tested-by: Bill Roman <bill.roman@datalight.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Adrian Bunk <bunk@kernel.org>

diff --git a/fs/namei.c b/fs/namei.c
index 3ece3a93dd926c9c2ddf22168125bf9532586d98..0d2d26823f7b2a4de2f3f36f6f502a37551d388c 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1489,7 +1489,7 @@ int may_open(struct nameidata *nd, int acc_mode, int flag)
        if (S_ISLNK(inode->i_mode))
                return -ELOOP;
        
-       if (S_ISDIR(inode->i_mode) && (flag & FMODE_WRITE))
+       if (S_ISDIR(inode->i_mode) && (acc_mode & MAY_WRITE))
                return -EISDIR;
 
        error = vfs_permission(nd, acc_mode);
@@ -1508,7 +1508,7 @@ int may_open(struct nameidata *nd, int acc_mode, int flag)
                        return -EACCES;
 
                flag &= ~O_TRUNC;
-       } else if (IS_RDONLY(inode) && (flag & FMODE_WRITE))
+       } else if (IS_RDONLY(inode) && (acc_mode & MAY_WRITE))
                return -EROFS;
        /*
         * An append-only file must be opened in append mode for writing.