From: Filipe Manana fdmanana@suse.com
commit e60aa5da14d01fed8411202dbe4adf6c44bd2a57 upstream.
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 against the directory.
This can be reproduced by the following C program provided by Ian Johnson:
#include <dirent.h> #include <stdio.h>
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; }
Reported-by: Ian Johnson ian@ianjohnson.dev Link: https://lore.kernel.org/linux-btrfs/YR1P0S.NGASEG570GJ8@ianjohnson.dev/ Fixes: 9b378f6ad48c ("btrfs: fix infinite directory reads") CC: stable@vger.kernel.org # 6.5+ Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com --- 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 6f388fee0eee..aeae04b5cef4 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -6049,6 +6049,19 @@ 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; @@ -11429,7 +11442,7 @@ 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,