[v13,1/5] overlayfs: check CAP_DAC_READ_SEARCH before issuing exportfs_decode_fh

Commit Message

Mark Salyzyn July 31, 2019, 4:57 p.m. UTC

Assumption never checked, should fail if the mounter creds are not
sufficient.

Signed-off-by: Mark Salyzyn <[e-mail]>
Cc: Miklos Szeredi <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Vivek Goyal <[e-mail]>
Cc: Eric W. Biederman <[e-mail]>
Cc: Amir Goldstein <[e-mail]>
Cc: Randy Dunlap <[e-mail]>
Cc: Stephen Smalley <[e-mail]>
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Cc: Eric Van Hensbergen <[e-mail]>
Cc: Latchesar Ionkov <[e-mail]>
Cc: Dominique Martinet <[e-mail]>
Cc: David Howells <[e-mail]>
Cc: Chris Mason <[e-mail]>
Cc: Josef Bacik <[e-mail]>
Cc: David Sterba <[e-mail]>
Cc: Jeff Layton <[e-mail]>
Cc: Sage Weil <[e-mail]>
Cc: Ilya Dryomov <[e-mail]>
Cc: Steve French <[e-mail]>
Cc: Tyler Hicks <[e-mail]>
Cc: Jan Kara <[e-mail]>
Cc: Theodore Ts'o <[e-mail]>
Cc: Andreas Dilger <[e-mail]>
Cc: Jaegeuk Kim <[e-mail]>
Cc: Chao Yu <[e-mail]>
Cc: Bob Peterson <[e-mail]>
Cc: Andreas Gruenbacher <[e-mail]>
Cc: David Woodhouse <[e-mail]>
Cc: Richard Weinberger <[e-mail]>
Cc: Dave Kleikamp <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Tejun Heo <[e-mail]>
Cc: Trond Myklebust <[e-mail]>
Cc: Anna Schumaker <[e-mail]>
Cc: Mark Fasheh <[e-mail]>
Cc: Joel Becker <[e-mail]>
Cc: Joseph Qi <[e-mail]>
Cc: Mike Marshall <[e-mail]>
Cc: Martin Brandenburg <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Phillip Lougher <[e-mail]>
Cc: Darrick J. Wong <[e-mail]>
Cc: [e-mail]
Cc: Hugh Dickins <[e-mail]>
Cc: David S. Miller <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Mathieu Malaterre <[e-mail]>
Cc: Ernesto A. Fernández <[e-mail]>
Cc: Vyacheslav Dubeyko <[e-mail]>
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Cc: [e-mail] # 4.4, 4.9, 4.14 & 4.19
---
v11 + v12 + v13 - rebase

v10:
- return NULL rather than ERR_PTR(-EPERM)
- did _not_ add it ovl_can_decode_fh() because of changes since last
  review, suspect needs to be added to ovl_lower_uuid_ok()?

v8 + v9:
- rebase

v7:
- This time for realz

v6:
- rebase

v5:
- dependency of "overlayfs: override_creds=off option bypass creator_cred"
---
 fs/overlayfs/namei.c | 3 +++
 1 file changed, 3 insertions(+)

Patch

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index e9717c2f7d45..9702f0d5309d 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -161,6 +161,9 @@  struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt,
 	if (!uuid_equal(&fh->uuid, &mnt->mnt_sb->s_uuid))
 		return NULL;
 
+	if (!capable(CAP_DAC_READ_SEARCH))
+		return NULL;
+
 	bytes = (fh->len - offsetof(struct ovl_fh, fid));
 	real = exportfs_decode_fh(mnt, (struct fid *)fh->fid,
 				  bytes >> 2, (int)fh->type,