On Thu, Jul 11, 2019 at 5:00 PM Jan Kara <jack@xxxxxxx> 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> > --- Looks sane. (I'll let xfs developers offer reviewed-by tags) > fs/xfs/xfs_file.c | 20 ++++++++++++++++++++ > 1 file changed, 20 insertions(+) > > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c > index 76748255f843..88fe3dbb3ba2 100644 > --- a/fs/xfs/xfs_file.c > +++ b/fs/xfs/xfs_file.c > @@ -33,6 +33,7 @@ > #include <linux/pagevec.h> > #include <linux/backing-dev.h> > #include <linux/mman.h> > +#include <linux/fadvise.h> > > static const struct vm_operations_struct xfs_file_vm_ops; > > @@ -939,6 +940,24 @@ 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; > + > + /* Readahead needs protection from hole punching and similar ops */ > + if (advice == POSIX_FADV_WILLNEED) > + xfs_ilock(ip, XFS_IOLOCK_SHARED); > + ret = generic_fadvise(file, start, end, advice); > + if (advice == POSIX_FADV_WILLNEED) > + xfs_iunlock(ip, XFS_IOLOCK_SHARED); > + return ret; > +} > > STATIC loff_t > xfs_file_remap_range( > @@ -1235,6 +1254,7 @@ 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 >
