From f2e0f18c8bd9c6d61575a2311d488e21831e1163 Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Sat, 9 Sep 2023 12:12:14 +0100 Subject: [PATCH 7/9] btrfs: refresh dir last index during a rewinddir(3) call When opening a directory we find what's the index of its last entry and then store it in the directory's file handle private data (struct btrfs_file_private::last_index), so that in the case new directory entries are added to a directory after an opendir(3) call we don't end up in an infinite loop (see commit 9b378f6ad48c ("btrfs: fix infinite directory reads")) when calling readdir(3). However once rewinddir(3) is called, POSIX states [1] that any new directory entries added after the previous opendir(3) call, must be returned by subsequent calls to readdir(3): "The rewinddir() function shall reset the position of the directory stream to which dirp refers to the beginning of the directory. It shall also cause the directory stream to refer to the current state of the corresponding directory, as a call to opendir() would have done." We currently don't refresh the last_index field of the struct btrfs_file_private associated to the directory, so after a rewinddir(3) we are not returning any new entries added after the opendir(3) call. Fix this by finding the current last index of the directory when llseek is called agains the directory. This can be reproduced by the following C program provided by Ian Johnson: #include #include int main(void) { DIR *dir = opendir("test"); FILE *file; file = fopen("test/1", "w"); fwrite("1", 1, 1, file); fclose(file); file = fopen("test/2", "w"); fwrite("2", 1, 1, file); fclose(file); rewinddir(dir); struct dirent *entry; while ((entry = readdir(dir))) { printf("%s\n", entry->d_name); } closedir(dir); return 0; } [1] https://pubs.opengroup.org/onlinepubs/9699919799/functions/rewinddir.html Reported-by: Ian Johnson Link: https://lore.kernel.org/linux-btrfs/YR1P0S.NGASEG570GJ8@ianjohnson.dev/ Fixes: 9b378f6ad48c ("btrfs: fix infinite directory reads") Signed-off-by: Filipe Manana --- fs/btrfs/inode.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index e3a52438f4f1..a50cbcafca03 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -5973,6 +5973,19 @@ static int btrfs_opendir(struct inode *inode, struct file *file) return 0; } +static loff_t btrfs_dir_llseek(struct file *file, loff_t offset, int whence) +{ + struct btrfs_file_private *private = file->private_data; + int ret; + + ret = btrfs_get_dir_last_index(BTRFS_I(file_inode(file)), + &private->last_index); + if (ret) + return ret; + + return generic_file_llseek(file, offset, whence); +} + struct dir_entry { u64 ino; u64 offset; @@ -11053,7 +11066,7 @@ static const struct inode_operations btrfs_dir_inode_operations = { }; static const struct file_operations btrfs_dir_file_operations = { - .llseek = generic_file_llseek, + .llseek = btrfs_dir_llseek, .read = generic_read_dir, .iterate_shared = btrfs_real_readdir, .open = btrfs_opendir, -- 2.42.0