From 8d6c121018bf60d631c05a4a2efc468a392b97bb Mon Sep 17 00:00:00 2001 From: Eric Sandeen Date: Thu, 17 Apr 2014 08:15:28 +1000 Subject: [PATCH] xfs: fix buffer use after free on IO error When testing exhaustion of dm snapshots, the following appeared with CONFIG_DEBUG_OBJECTS_FREE enabled: ODEBUG: free active (active state 0) object type: work_struct hint: xfs_buf_iodone_work+0x0/0x1d0 [xfs] indicating that we'd freed a buffer which still had a pending reference, down this path: [ 190.867975] [] debug_check_no_obj_freed+0x22b/0x270 [ 190.880820] [] kmem_cache_free+0xd0/0x370 [ 190.892615] [] xfs_buf_free+0xe4/0x210 [xfs] [ 190.905629] [] xfs_buf_rele+0xe7/0x270 [xfs] [ 190.911770] [] xfs_trans_read_buf_map+0x7b6/0xac0 [xfs] At issue is the fact that if IO fails in xfs_buf_iorequest, we'll queue completion unconditionally, and then call xfs_buf_rele; but if IO failed, there are no IOs remaining, and xfs_buf_rele will free the bp while work is still queued. Fix this by not scheduling completion if the buffer has an error on it; run it immediately. The rest is only comment changes. Thanks to dchinner for spotting the root cause. Signed-off-by: Eric Sandeen Reviewed-by: Brian Foster Signed-off-by: Dave Chinner --- fs/xfs/xfs_buf.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index 107f2fdfe41f..cb10a0aaab3a 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -1372,21 +1372,29 @@ xfs_buf_iorequest( xfs_buf_wait_unpin(bp); xfs_buf_hold(bp); - /* Set the count to 1 initially, this will stop an I/O + /* + * Set the count to 1 initially, this will stop an I/O * completion callout which happens before we have started * all the I/O from calling xfs_buf_ioend too early. */ atomic_set(&bp->b_io_remaining, 1); _xfs_buf_ioapply(bp); - _xfs_buf_ioend(bp, 1); + /* + * If _xfs_buf_ioapply failed, we'll get back here with + * only the reference we took above. _xfs_buf_ioend will + * drop it to zero, so we'd better not queue it for later, + * or we'll free it before it's done. + */ + _xfs_buf_ioend(bp, bp->b_error ? 0 : 1); xfs_buf_rele(bp); } /* * Waits for I/O to complete on the buffer supplied. It returns immediately if - * no I/O is pending or there is already a pending error on the buffer. It - * returns the I/O error code, if any, or 0 if there was no error. + * no I/O is pending or there is already a pending error on the buffer, in which + * case nothing will ever complete. It returns the I/O error code, if any, or + * 0 if there was no error. */ int xfs_buf_iowait( -- 2.30.2