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    Subject[PATCH 5.4 06/47] f2fs: prevent creating duplicate encrypted filenames
    Date
    From: Eric Biggers <ebiggers@google.com>

    commit bfc2b7e8518999003a61f91c1deb5e88ed77b07d upstream.

    As described in "fscrypt: add fscrypt_is_nokey_name()", it's possible to
    create a duplicate filename in an encrypted directory by creating a file
    concurrently with adding the directory's encryption key.

    Fix this bug on f2fs by rejecting no-key dentries in f2fs_add_link().

    Note that the weird check for the current task in f2fs_do_add_link()
    seems to make this bug difficult to reproduce on f2fs.

    Fixes: 9ea97163c6da ("f2fs crypto: add filename encryption for f2fs_add_link")
    Cc: stable@vger.kernel.org
    Link: https://lore.kernel.org/r/20201118075609.120337-4-ebiggers@kernel.org
    Signed-off-by: Eric Biggers <ebiggers@google.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    fs/f2fs/f2fs.h | 2 ++
    1 file changed, 2 insertions(+)

    --- a/fs/f2fs/f2fs.h
    +++ b/fs/f2fs/f2fs.h
    @@ -2998,6 +2998,8 @@ bool f2fs_empty_dir(struct inode *dir);

    static inline int f2fs_add_link(struct dentry *dentry, struct inode *inode)
    {
    + if (fscrypt_is_nokey_name(dentry))
    + return -ENOKEY;
    return f2fs_do_add_link(d_inode(dentry->d_parent), &dentry->d_name,
    inode, inode->i_ino, inode->i_mode);
    }

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