btrfs: fix fallocate to use file_modified to update permissions consistently

BugLink: https://bugs.launchpad.net/bugs/1969857
[ Upstream commit 05fd9564e9faf0f23b4676385e27d9405cef6637 ]

Since the initial introduction of (posix) fallocate back at the turn of
the century, it has been possible to use this syscall to change the
user-visible contents of files.  This can happen by extending the file
size during a preallocation, or through any of the newer modes (punch,
zero range).  Because the call can be used to change file contents, we
should treat it like we do any other modification to a file -- update
the mtime, and drop set[ug]id privileges/capabilities.

The VFS function file_modified() does all this for us if pass it a
locked inode, so let's make fallocate drop permissions correctly.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index a1762363f61faff8248c9fc4e7cda9503c775da5..dc1e4d1b72914427e9ae23662c5f1eb5c6a0ca0a 100644 (file)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2878,8 +2878,9 @@ out:
        return ret;
 }
 
-static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
+static int btrfs_punch_hole(struct file *file, loff_t offset, loff_t len)
 {
+       struct inode *inode = file_inode(file);
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct extent_state *cached_state = NULL;
@@ -2911,6 +2912,10 @@ static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
                goto out_only_mutex;
        }
 
+       ret = file_modified(file);
+       if (ret)
+               goto out_only_mutex;
+
        lockstart = round_up(offset, btrfs_inode_sectorsize(BTRFS_I(inode)));
        lockend = round_down(offset + len,
                             btrfs_inode_sectorsize(BTRFS_I(inode))) - 1;
@@ -3351,7 +3356,7 @@ static long btrfs_fallocate(struct file *file, int mode,
                return -EOPNOTSUPP;
 
        if (mode & FALLOC_FL_PUNCH_HOLE)
-               return btrfs_punch_hole(inode, offset, len);
+               return btrfs_punch_hole(file, offset, len);
 
        /*
         * Only trigger disk allocation, don't trigger qgroup reserve
@@ -3373,6 +3378,10 @@ static long btrfs_fallocate(struct file *file, int mode,
                        goto out;
        }
 
+       ret = file_modified(file);
+       if (ret)
+               goto out;
+
        /*
         * TODO: Move these two operations after we have checked
         * accurate reserved space, or fallocate can still fail but