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btrfs: fix fallocate to use file_modified to update permissions consistently

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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>
This commit is contained in:
Darrick J. Wong 2022-03-14 10:55:32 -07:00 committed by David Sterba
parent bbac58698a
commit 05fd9564e9
1 changed files with 11 additions and 2 deletions
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13
fs/btrfs/file.c
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@ -2957,8 +2957,9 @@ 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;
@ -2990,6 +2991,10 @@ 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;
@ -3430,7 +3435,7 @@ 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
@ -3452,6 +3457,10 @@ 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