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authorMiklos Szeredi <mszeredi@redhat.com>2020-12-14 15:26:14 +0100
committerMiklos Szeredi <mszeredi@redhat.com>2020-12-14 15:26:14 +0100
commitc846af050f944d584f28bc0de310383003c8096d (patch)
tree32070dcfc93dd4164928c5d7056836f5c420bfc7 /fs/overlayfs
parent3078d85c9a1099405a0463c4d112ba97ee5bd217 (diff)
ovl: check privs before decoding file handle
CAP_DAC_READ_SEARCH is required by open_by_handle_at(2) so check it in ovl_decode_real_fh() as well to prevent privilege escalation for unprivileged overlay mounts. [Amir] If the mounter is not capable in init ns, ovl_check_origin() and ovl_verify_index() will not function as expected and this will break index and nfs export features. So check capability in ovl_can_decode_fh(), to auto disable those features. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'fs/overlayfs')
-rw-r--r--fs/overlayfs/namei.c3
-rw-r--r--fs/overlayfs/util.c3
2 files changed, 6 insertions, 0 deletions
diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 509dac77af61..3fe05fb5d145 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -156,6 +156,9 @@ struct dentry *ovl_decode_real_fh(struct ovl_fs *ofs, struct ovl_fh *fh,
struct dentry *real;
int bytes;
+ if (!capable(CAP_DAC_READ_SEARCH))
+ return NULL;
+
/*
* Make sure that the stored uuid matches the uuid of the lower
* layer where file handle will be decoded.
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 44b4b62a8ac8..ced63c79e9dd 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -50,6 +50,9 @@ const struct cred *ovl_override_creds(struct super_block *sb)
*/
int ovl_can_decode_fh(struct super_block *sb)
{
+ if (!capable(CAP_DAC_READ_SEARCH))
+ return 0;
+
if (!sb->s_export_op || !sb->s_export_op->fh_to_dentry)
return 0;