generic_permission: MAY_OPEN is not write access

commit 7ea6600148c265b1fd53e521022b1d7aec81d974 upstream.

generic_permission was refusing CAP_DAC_READ_SEARCH-enabled
processes from opening DAC-protected files read-only, because
do_filp_open adds MAY_OPEN to the open mask.

Ignore MAY_OPEN.  After this patch, CAP_DAC_READ_SEARCH is
again sufficient to open(fname, O_RDONLY) on a file to which
DAC otherwise refuses us read permission.

Reported-by: Mike Kazantsev <mk.fraggod@gmail.com>
Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Tested-by: Mike Kazantsev <mk.fraggod@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/namei.c b/fs/namei.c
index 2259d21ae2818e0767dea0a4dcd89c6fe757d009..e6c73de3a8adcf84d13fa4c489e98a19dbc31272 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -220,6 +220,7 @@ int generic_permission(struct inode *inode, int mask,
        /*
         * Searching includes executable on directories, else just read.
         */
+       mask &= MAY_READ | MAY_WRITE | MAY_EXEC;
        if (mask == MAY_READ || (S_ISDIR(inode->i_mode) && !(mask & MAY_WRITE)))
                if (capable(CAP_DAC_READ_SEARCH))
                        return 0;