On Thu, Aug 29, 2019 at 03:10:34PM +0200, Jan Kara wrote: > Hole puching currently evicts pages from page cache and then goes on to > remove blocks from the inode. This happens under both XFS_IOLOCK_EXCL > and XFS_MMAPLOCK_EXCL which provides appropriate serialization with > racing reads or page faults. However there is currently nothing that > prevents readahead triggered by fadvise() or madvise() from racing with > the hole punch and instantiating page cache page after hole punching has > evicted page cache in xfs_flush_unmap_range() but before it has removed > blocks from the inode. This page cache page will be mapping soon to be > freed block and that can lead to returning stale data to userspace or > even filesystem corruption. > > Fix the problem by protecting handling of readahead requests by > XFS_IOLOCK_SHARED similarly as we protect reads. > > CC: stable@xxxxxxxxxxxxxxx > Link: https://lore.kernel.org/linux-fsdevel/CAOQ4uxjQNmxqmtA_VbYW0Su9rKRk2zobJmahcyeaEVOFKVQ5dw@xxxxxxxxxxxxxx/ > Reported-by: Amir Goldstein <amir73il@xxxxxxxxx> > Signed-off-by: Jan Kara <jack@xxxxxxx> Is there a test on xfstests to demonstrate this race? Will test it out though... Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> --D > --- > fs/xfs/xfs_file.c | 26 ++++++++++++++++++++++++++ > 1 file changed, 26 insertions(+) > > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c > index 28101bbc0b78..d952d5962e93 100644 > --- a/fs/xfs/xfs_file.c > +++ b/fs/xfs/xfs_file.c > @@ -28,6 +28,7 @@ > #include <linux/falloc.h> > #include <linux/backing-dev.h> > #include <linux/mman.h> > +#include <linux/fadvise.h> > > static const struct vm_operations_struct xfs_file_vm_ops; > > @@ -933,6 +934,30 @@ xfs_file_fallocate( > return error; > } > > +STATIC int > +xfs_file_fadvise( > + struct file *file, > + loff_t start, > + loff_t end, > + int advice) > +{ > + struct xfs_inode *ip = XFS_I(file_inode(file)); > + int ret; > + int lockflags = 0; > + > + /* > + * Operations creating pages in page cache need protection from hole > + * punching and similar ops > + */ > + if (advice == POSIX_FADV_WILLNEED) { > + lockflags = XFS_IOLOCK_SHARED; > + xfs_ilock(ip, lockflags); > + } > + ret = generic_fadvise(file, start, end, advice); > + if (lockflags) > + xfs_iunlock(ip, lockflags); > + return ret; > +} > > STATIC loff_t > xfs_file_remap_range( > @@ -1232,6 +1257,7 @@ const struct file_operations xfs_file_operations = { > .fsync = xfs_file_fsync, > .get_unmapped_area = thp_get_unmapped_area, > .fallocate = xfs_file_fallocate, > + .fadvise = xfs_file_fadvise, > .remap_file_range = xfs_file_remap_range, > }; > > -- > 2.16.4 >
