For overlay file open, check IS_APPEND() on the real upper inode
inside d_real(), because the overlay inode does not have the
S_APPEND flag and IS_APPEND() can only be checked at open time.
Note that because overlayfs does not copy up the chattr inode flags
(i.e. S_APPEND, S_IMMUTABLE), the IS_APPEND() check is only relevant
for upper inodes that were set with chattr +a and not to lower
inodes that had chattr +a before copy up.
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/overlayfs/super.c | 28 +++++++++++++++++++++++++---
1 file changed, 25 insertions(+), 3 deletions(-)
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index c9e70d3..c072a0c 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -49,11 +49,28 @@ static void ovl_dentry_release(struct dentry *dentry)
}
}
+static int ovl_check_append_only(struct inode *inode, int flag)
+{
+ /*
+ * This test was moot in vfs may_open() because overlay inode does
+ * not have the S_APPEND flag, so re-check on real upper inode
+ */
+ if (IS_APPEND(inode)) {
+ if ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND))
+ return -EPERM;
+ if (flag & O_TRUNC)
+ return -EPERM;
+ }
+
+ return 0;
+}
+
static struct dentry *ovl_d_real(struct dentry *dentry,
const struct inode *inode,
unsigned int open_flags)
{
struct dentry *real;
+ int err;
if (!d_is_reg(dentry)) {
if (!inode || inode == d_inode(dentry))
@@ -65,15 +82,20 @@ static struct dentry *ovl_d_real(struct dentry *dentry,
return dentry;
if (open_flags) {
- int err = ovl_open_maybe_copy_up(dentry, open_flags);
-
+ err = ovl_open_maybe_copy_up(dentry, open_flags);
if (err)
return ERR_PTR(err);
}
real = ovl_dentry_upper(dentry);
- if (real && (!inode || inode == d_inode(real)))
+ if (real && (!inode || inode == d_inode(real))) {
+ if (!inode) {
+ err = ovl_check_append_only(d_inode(real), open_flags);
+ if (err)
+ return ERR_PTR(err);
+ }
return real;
+ }
real = ovl_dentry_lower(dentry);
if (!real)
--
2.7.4
--
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