Hi, Please note that -CURRENT in revision range of [r286951, 287283), approximately 9 days ago until now, are affected by a buffer overrun issue that may cause data corruption (!) which may manifest itself as random panics that relates to NULL pointer deference (e.g. Kernel Trap 12 with <4K fault address), or strange UMA related panics. Systems that do not have L2ARC devices are not affected by this problem. The affected code is L2ARC specific. For those who are using L2ARC devices -- it's not clear to me how bad the corruption could affect the on disk data for ZFS. If you are running -CURRENT and have L2ARC, please be sure to examine if you have any data loss. Cheers, -------- Forwarded Message -------- Subject: svn commit: r287283 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs Date: Sat, 29 Aug 2015 09:22:33 +0000 (UTC) From: Xin LI <delphij_at_FreeBSD.org> To: src-committers_at_freebsd.org, svn-src-all_at_freebsd.org, svn-src-head_at_freebsd.org Author: delphij Date: Sat Aug 29 09:22:32 2015 New Revision: 287283 URL: https://svnweb.freebsd.org/changeset/base/287283 Log: Fix a buffer overrun which may lead to data corruption, introduced in r286951 by reinstating changes in r274628. In l2arc_compress_buf(), we allocate a buffer to stash away the compressed data in 'cdata', allocated of l2hdr->b_asize bytes. We then ask zio_compress_data() to compress the buffer, b_l1hdr.b_tmp_cdata, which is of l2hdr->b_asize bytes, and have the compressed size (or original size, if compress didn't gain enough) stored in csize. To pad the buffer to fit the optimal write size, we round up the compressed size to L2 device's vdev_ashift. Illumos code rounds up the size by at most SPA_MINBLOCKSIZE. Because we know csize <= b_asize, and b_asize is integer multiple of SPA_MINBLOCKSIZE, we are guaranteed that the rounded up csize would be <= b_asize. However, this is not necessarily true when we round up to 1 << vdev_ashift, because it could be larger than SPA_MINBLOCKSIZE. So, in the worst case scenario, we are overwriting at most (1 << vdev_ashift - SPA_MINBLOCKSIZE) bytes of memory next to the compressed data buffer. Andriy's original change in r274628 reorganized the code a little bit, by moving the padding to after we determined that the compression was beneficial. At which point, we would check rounded size against the allocated buffer size, and the buffer overrun would not be possible. Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c Cheers,
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