[PATCH 5.17 131/219] btrfs: fix fallocate to use file_modified to update permissions consistently

Greg Kroah-Hartman
2022-04-18T12:31:16Z

From: Darrick J. Wong <djwong@kernel.org>

[ 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>
---
fs/btrfs/file.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index a0179cc62913..28ddd9cf2069 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2918,8 +2918,9 @@ int btrfs_replace_file_extents(struct btrfs_inode *inode,
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;
@@ -2951,6 +2952,10 @@ 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;
@@ -3391,7 +3396,7 @@ 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
@@ -3413,6 +3418,10 @@ 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
--
2.35.1