On Mon, Mar 30, 2009 at 03:20:24PM -0400, Mikulas Patocka wrote: > Hi > > I'm submitting this patch for 2.6.30 merge window. > > > FAT filesystem used down_read(&mapping->host->i_alloc_sem) to prevent > a race between bmap and truncate. However, such race is present in all the > other filesystems --- it is generally assumed that blocks queried with > get_block won't disappear while get_block is in progress. > > The race can be only triggered by root, non-privileged users can't use > bmap, so it is not a security issue (unless there is some program run > by root that bmaps users' files). > > This patch fixes the race in a generic way, in all the filesystems. If some > filesystem employs its own locking and doesn't want to take i_alloc_sem > (I don't know about any, where taking i_alloc_sem could be problem), > let it use its own function and not generic_block_bmap. > > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> > > --- > fs/buffer.c | 8 ++++++++ > fs/fat/inode.c | 2 -- > 2 files changed, 8 insertions(+), 2 deletions(-) > > Index: linux-2.6.29-devel/fs/buffer.c > =================================================================== > --- linux-2.6.29-devel.orig/fs/buffer.c 2009-03-29 04:48:38.000000000 +0200 > +++ linux-2.6.29-devel/fs/buffer.c 2009-03-29 05:26:53.000000000 +0200 > @@ -2963,7 +2963,15 @@ sector_t generic_block_bmap(struct addre > tmp.b_state = 0; > tmp.b_blocknr = 0; > tmp.b_size = 1 << inode->i_blkbits; > + > + /* > + * Protect the inode from being truncated while get_block is > + * in progress. > + */ > + down_read(&mapping->host->i_alloc_sem); > get_block(inode, block, &tmp, 0); > + up_read(&mapping->host->i_alloc_sem); > + > return tmp.b_blocknr; > } > > Index: linux-2.6.29-devel/fs/fat/inode.c > =================================================================== > --- linux-2.6.29-devel.orig/fs/fat/inode.c 2009-03-29 04:46:35.000000000 +0200 > +++ linux-2.6.29-devel/fs/fat/inode.c 2009-03-29 05:26:53.000000000 +0200 > @@ -202,9 +202,7 @@ static sector_t _fat_bmap(struct address > sector_t blocknr; > > /* fat_get_cluster() assumes the requested blocknr isn't truncated. */ > - down_read(&mapping->host->i_alloc_sem); > blocknr = generic_block_bmap(mapping, block, fat_get_block); > - up_read(&mapping->host->i_alloc_sem); > > return blocknr; > } ext4_inode_info.i_data_sem should protect against get_block and truncate race . On ext3 ext3_inode_info.truncate_mutex should do the same. We already take these locks in get_block -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
