commit: 3eaf9cc62f447a742b26fa601993e94406aa1ea1
When the filesystem is created without a journal, we eventually call
into __generic_file_fsync() in order to write out all the modified
in-core data to the permanent storage device. This function happens to
try and obtain an inode_lock() while synchronizing the files buffer
and it's associated metadata.
Generally, this is fine, however it becomes a problem when there is
higher level code that has already obtained an inode_lock() as this
leads to a recursive lock situation. This case is especially true when
porting across direct I/O to iomap infrastructure as we obtain an
inode_lock() early on in the I/O within ext4_dio_write_iter() and hold
it until the I/O has been completed. Consequently, to not run into
this specific issue, we move away from calling into
__generic_file_fsync() and perform the necessary synchronization tasks
within ext4_sync_file().
Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
commit 08adf452e628b0e2ce9a01048cfbec52353703d7 upstream.
'igrab(d_inode(dentry->d_parent))' without holding dentry->d_lock is
broken because without d_lock, d_parent can be concurrently changed due
to a rename(). Then if the old directory is immediately deleted, old
d_parent->inode can be NULL. That causes a NULL dereference in igrab().
To fix this, use dget_parent() to safely grab a reference to the parent
dentry, which pins the inode. This also eliminates the need to use
d_find_any_alias() other than for the initial inode, as we no longer
throw away the dentry at each step.
This is an extremely hard race to hit, but it is possible. Adding a
udelay() in between the reads of ->d_parent and its ->d_inode makes it
reproducible on a no-journal filesystem using the following program:
#include <fcntl.h>
#include <unistd.h>
int main()
{
if (fork()) {
for (;;) {
mkdir("dir1", 0700);
int fd = open("dir1/file", O_RDWR|O_CREAT|O_SYNC);
write(fd, "X", 1);
close(fd);
}
} else {
mkdir("dir2", 0700);
for (;;) {
rename("dir1/file", "dir2/file");
rmdir("dir1");
}
}
}
Fixes: d59729f4e794 ("ext4: fix races in ext4_sync_parent()")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20200506183140.541194-1-ebiggers@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Peng Hao