Message ID | 20200917051341.9811-2-hsiangkao@redhat.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | xfs: random patches on log recovery | expand |
On Thu, Sep 17, 2020 at 01:13:40PM +0800, Gao Xiang wrote: > Currently, crafted h_len has been blocked for the log > header of the tail block in commit a70f9fe52daa ("xfs: > detect and handle invalid iclog size set by mkfs"). > > However, each log record could still have crafted h_len > and cause log record buffer overrun. So let's check > h_len vs buffer size for each log record as well. > > Signed-off-by: Gao Xiang <hsiangkao@redhat.com> > --- > v3: https://lore.kernel.org/r/20200904082516.31205-2-hsiangkao@redhat.com > > changes since v3: > - drop exception comment to avoid confusion (Brian); > - check rhead->hlen vs buffer size to address > the harmful overflow (Brian); > > And as Brian requested previously, "Also, please test the workaround > case to make sure it still works as expected (if you haven't already)." > > So I tested the vanilla/after upstream kernels with compiled xfsprogs-v4.3.0, > which was before mkfs fix 20fbd4593ff2 ("libxfs: format the log with > valid log record headers") got merged, and I generated a questionable > image followed by the instruction described in the related commit > messages with "mkfs.xfs -dsunit=512,swidth=4096 -f test.img" and > logprint says > > cycle: 1 version: 2 lsn: 1,0 tail_lsn: 1,0 > length of Log Record: 261632 prev offset: -1 num ops: 1 > uuid: 7b84cd80-7855-4dc8-91ce-542c7d65ba99 format: little endian linux > h_size: 32768 > > so "length of Log Record" is overrun obviously, but I cannot reproduce > the described workaround case for vanilla/after kernels anymore. > > I think the reason is due to commit 7f6aff3a29b0 ("xfs: only run torn > log write detection on dirty logs"), which changes the behavior > described in commit a70f9fe52daa8 ("xfs: detect and handle invalid > iclog size set by mkfs") from "all records at the head of the log > are verified for CRC errors" to "we can only run CRC verification > when the log is dirty because there's no guarantee that the log > data behind an unmount record is compatible with the current > architecture).", more details see codediff of a70f9fe52daa8. > If I follow correctly, you're saying that prior to commit 7f6aff3a29b0, log recovery would run a CRC pass on a clean log (with an unmount record) and this is where the old workaround code would kick in if the filesystem happened to be misformatted by mkfs. After said commit, the CRC pass is no longer run unless the log is dirty (for arch compatibility reasons), so we fall into the xlog_check_unmount_rec() path that does some careful (presumably arch agnostic) detection of a clean/dirty log based on whether the record just behind the head has a single unmount transaction. This function already uses h_len properly and only reads a single log block to determine whether the target is an unmount record, so doesn't have the same overflow risk as a full recovery pass. Am I following that correctly? If so, the patch otherwise looks reasonable to me: Reviewed-by: Brian Foster <bfoster@redhat.com> > The timeline seems to be: > https://lore.kernel.org/r/1447342648-40012-1-git-send-email-bfoster@redhat.com > a70f9fe52daa [PATCH v2 1/8] xfs: detect and handle invalid iclog size set by mkfs > 7088c4136fa1 [PATCH v2 7/8] xfs: detect and trim torn writes during log recovery > https://lore.kernel.org/r/1457008798-58734-5-git-send-email-bfoster@redhat.com > 7f6aff3a29b0 [PATCH 4/4] xfs: only run torn log write detection on dirty logs > > so IMHO, the workaround a70f9fe52daa would only be useful between > 7088c4136fa1 ~ 7f6aff3a29b0. > > Yeah, it relates to several old kernel commits/versions, my technical > analysis is as above. This patch doesn't actually change the real > original workaround logic. Even if the workground can be removed now, > that should be addressed with another patch and that is quite another > story. > > Kindly correct me if I'm wrong :-) > > Thanks, > Gao Xiang > > fs/xfs/xfs_log_recover.c | 39 +++++++++++++++++++-------------------- > 1 file changed, 19 insertions(+), 20 deletions(-) > > diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c > index a17d788921d6..782ec3eeab4d 100644 > --- a/fs/xfs/xfs_log_recover.c > +++ b/fs/xfs/xfs_log_recover.c > @@ -2878,7 +2878,8 @@ STATIC int > xlog_valid_rec_header( > struct xlog *log, > struct xlog_rec_header *rhead, > - xfs_daddr_t blkno) > + xfs_daddr_t blkno, > + int bufsize) > { > int hlen; > > @@ -2894,10 +2895,14 @@ xlog_valid_rec_header( > return -EFSCORRUPTED; > } > > - /* LR body must have data or it wouldn't have been written */ > + /* > + * LR body must have data (or it wouldn't have been written) > + * and h_len must not be greater than LR buffer size. > + */ > hlen = be32_to_cpu(rhead->h_len); > - if (XFS_IS_CORRUPT(log->l_mp, hlen <= 0 || hlen > INT_MAX)) > + if (XFS_IS_CORRUPT(log->l_mp, hlen <= 0 || hlen > bufsize)) > return -EFSCORRUPTED; > + > if (XFS_IS_CORRUPT(log->l_mp, > blkno > log->l_logBBsize || blkno > INT_MAX)) > return -EFSCORRUPTED; > @@ -2958,9 +2963,6 @@ xlog_do_recovery_pass( > goto bread_err1; > > rhead = (xlog_rec_header_t *)offset; > - error = xlog_valid_rec_header(log, rhead, tail_blk); > - if (error) > - goto bread_err1; > > /* > * xfsprogs has a bug where record length is based on lsunit but > @@ -2975,21 +2977,18 @@ xlog_do_recovery_pass( > */ > h_size = be32_to_cpu(rhead->h_size); > h_len = be32_to_cpu(rhead->h_len); > - if (h_len > h_size) { > - if (h_len <= log->l_mp->m_logbsize && > - be32_to_cpu(rhead->h_num_logops) == 1) { > - xfs_warn(log->l_mp, > + if (h_len > h_size && h_len <= log->l_mp->m_logbsize && > + rhead->h_num_logops == cpu_to_be32(1)) { > + xfs_warn(log->l_mp, > "invalid iclog size (%d bytes), using lsunit (%d bytes)", > - h_size, log->l_mp->m_logbsize); > - h_size = log->l_mp->m_logbsize; > - } else { > - XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_LOW, > - log->l_mp); > - error = -EFSCORRUPTED; > - goto bread_err1; > - } > + h_size, log->l_mp->m_logbsize); > + h_size = log->l_mp->m_logbsize; > } > > + error = xlog_valid_rec_header(log, rhead, tail_blk, h_size); > + if (error) > + goto bread_err1; > + > if ((be32_to_cpu(rhead->h_version) & XLOG_VERSION_2) && > (h_size > XLOG_HEADER_CYCLE_SIZE)) { > hblks = h_size / XLOG_HEADER_CYCLE_SIZE; > @@ -3070,7 +3069,7 @@ xlog_do_recovery_pass( > } > rhead = (xlog_rec_header_t *)offset; > error = xlog_valid_rec_header(log, rhead, > - split_hblks ? blk_no : 0); > + split_hblks ? blk_no : 0, h_size); > if (error) > goto bread_err2; > > @@ -3151,7 +3150,7 @@ xlog_do_recovery_pass( > goto bread_err2; > > rhead = (xlog_rec_header_t *)offset; > - error = xlog_valid_rec_header(log, rhead, blk_no); > + error = xlog_valid_rec_header(log, rhead, blk_no, h_size); > if (error) > goto bread_err2; > > -- > 2.18.1 >
Hi Brian, On Tue, Sep 22, 2020 at 11:22:12AM -0400, Brian Foster wrote: > On Thu, Sep 17, 2020 at 01:13:40PM +0800, Gao Xiang wrote: > > Currently, crafted h_len has been blocked for the log > > header of the tail block in commit a70f9fe52daa ("xfs: > > detect and handle invalid iclog size set by mkfs"). > > > > However, each log record could still have crafted h_len > > and cause log record buffer overrun. So let's check > > h_len vs buffer size for each log record as well. > > > > Signed-off-by: Gao Xiang <hsiangkao@redhat.com> > > --- > > v3: https://lore.kernel.org/r/20200904082516.31205-2-hsiangkao@redhat.com > > > > changes since v3: > > - drop exception comment to avoid confusion (Brian); > > - check rhead->hlen vs buffer size to address > > the harmful overflow (Brian); > > > > And as Brian requested previously, "Also, please test the workaround > > case to make sure it still works as expected (if you haven't already)." > > > > So I tested the vanilla/after upstream kernels with compiled xfsprogs-v4.3.0, > > which was before mkfs fix 20fbd4593ff2 ("libxfs: format the log with > > valid log record headers") got merged, and I generated a questionable > > image followed by the instruction described in the related commit > > messages with "mkfs.xfs -dsunit=512,swidth=4096 -f test.img" and > > logprint says > > > > cycle: 1 version: 2 lsn: 1,0 tail_lsn: 1,0 > > length of Log Record: 261632 prev offset: -1 num ops: 1 > > uuid: 7b84cd80-7855-4dc8-91ce-542c7d65ba99 format: little endian linux > > h_size: 32768 > > > > so "length of Log Record" is overrun obviously, but I cannot reproduce > > the described workaround case for vanilla/after kernels anymore. > > > > I think the reason is due to commit 7f6aff3a29b0 ("xfs: only run torn > > log write detection on dirty logs"), which changes the behavior > > described in commit a70f9fe52daa8 ("xfs: detect and handle invalid > > iclog size set by mkfs") from "all records at the head of the log > > are verified for CRC errors" to "we can only run CRC verification > > when the log is dirty because there's no guarantee that the log > > data behind an unmount record is compatible with the current > > architecture).", more details see codediff of a70f9fe52daa8. > > > > If I follow correctly, you're saying that prior to commit 7f6aff3a29b0, > log recovery would run a CRC pass on a clean log (with an unmount > record) and this is where the old workaround code would kick in if the > filesystem happened to be misformatted by mkfs. After said commit, the > CRC pass is no longer run unless the log is dirty (for arch > compatibility reasons), so we fall into the xlog_check_unmount_rec() > path that does some careful (presumably arch agnostic) detection of a > clean/dirty log based on whether the record just behind the head has a > single unmount transaction. This function already uses h_len properly > and only reads a single log block to determine whether the target is an > unmount record, so doesn't have the same overflow risk as a full > recovery pass. > > Am I following that correctly? If so, the patch otherwise looks > reasonable to me: Yeah, that is what I was trying to say. Thanks for the review! Thanks, Gao Xiang > > Reviewed-by: Brian Foster <bfoster@redhat.com> > > > The timeline seems to be: > > https://lore.kernel.org/r/1447342648-40012-1-git-send-email-bfoster@redhat.com > > a70f9fe52daa [PATCH v2 1/8] xfs: detect and handle invalid iclog size set by mkfs > > 7088c4136fa1 [PATCH v2 7/8] xfs: detect and trim torn writes during log recovery > > https://lore.kernel.org/r/1457008798-58734-5-git-send-email-bfoster@redhat.com > > 7f6aff3a29b0 [PATCH 4/4] xfs: only run torn log write detection on dirty logs > > > > so IMHO, the workaround a70f9fe52daa would only be useful between > > 7088c4136fa1 ~ 7f6aff3a29b0. > > > > Yeah, it relates to several old kernel commits/versions, my technical > > analysis is as above. This patch doesn't actually change the real > > original workaround logic. Even if the workground can be removed now, > > that should be addressed with another patch and that is quite another > > story. > > > > Kindly correct me if I'm wrong :-) > > > > Thanks, > > Gao Xiang
On Thu, Sep 17, 2020 at 01:13:40PM +0800, Gao Xiang wrote: > Currently, crafted h_len has been blocked for the log > header of the tail block in commit a70f9fe52daa ("xfs: > detect and handle invalid iclog size set by mkfs"). > > However, each log record could still have crafted h_len > and cause log record buffer overrun. So let's check > h_len vs buffer size for each log record as well. > > Signed-off-by: Gao Xiang <hsiangkao@redhat.com> /me squints real hard and thinks he understands what this patch does. Tighten up xlog_valid_rec_header, and add a new callsite in the middle of xlog_do_recovery_pass instead of the insufficient length checking. Assuming that's right, Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> --D > --- > v3: https://lore.kernel.org/r/20200904082516.31205-2-hsiangkao@redhat.com > > changes since v3: > - drop exception comment to avoid confusion (Brian); > - check rhead->hlen vs buffer size to address > the harmful overflow (Brian); > > And as Brian requested previously, "Also, please test the workaround > case to make sure it still works as expected (if you haven't already)." > > So I tested the vanilla/after upstream kernels with compiled xfsprogs-v4.3.0, > which was before mkfs fix 20fbd4593ff2 ("libxfs: format the log with > valid log record headers") got merged, and I generated a questionable > image followed by the instruction described in the related commit > messages with "mkfs.xfs -dsunit=512,swidth=4096 -f test.img" and > logprint says > > cycle: 1 version: 2 lsn: 1,0 tail_lsn: 1,0 > length of Log Record: 261632 prev offset: -1 num ops: 1 > uuid: 7b84cd80-7855-4dc8-91ce-542c7d65ba99 format: little endian linux > h_size: 32768 > > so "length of Log Record" is overrun obviously, but I cannot reproduce > the described workaround case for vanilla/after kernels anymore. > > I think the reason is due to commit 7f6aff3a29b0 ("xfs: only run torn > log write detection on dirty logs"), which changes the behavior > described in commit a70f9fe52daa8 ("xfs: detect and handle invalid > iclog size set by mkfs") from "all records at the head of the log > are verified for CRC errors" to "we can only run CRC verification > when the log is dirty because there's no guarantee that the log > data behind an unmount record is compatible with the current > architecture).", more details see codediff of a70f9fe52daa8. > > The timeline seems to be: > https://lore.kernel.org/r/1447342648-40012-1-git-send-email-bfoster@redhat.com > a70f9fe52daa [PATCH v2 1/8] xfs: detect and handle invalid iclog size set by mkfs > 7088c4136fa1 [PATCH v2 7/8] xfs: detect and trim torn writes during log recovery > https://lore.kernel.org/r/1457008798-58734-5-git-send-email-bfoster@redhat.com > 7f6aff3a29b0 [PATCH 4/4] xfs: only run torn log write detection on dirty logs > > so IMHO, the workaround a70f9fe52daa would only be useful between > 7088c4136fa1 ~ 7f6aff3a29b0. > > Yeah, it relates to several old kernel commits/versions, my technical > analysis is as above. This patch doesn't actually change the real > original workaround logic. Even if the workground can be removed now, > that should be addressed with another patch and that is quite another > story. > > Kindly correct me if I'm wrong :-) > > Thanks, > Gao Xiang > > fs/xfs/xfs_log_recover.c | 39 +++++++++++++++++++-------------------- > 1 file changed, 19 insertions(+), 20 deletions(-) > > diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c > index a17d788921d6..782ec3eeab4d 100644 > --- a/fs/xfs/xfs_log_recover.c > +++ b/fs/xfs/xfs_log_recover.c > @@ -2878,7 +2878,8 @@ STATIC int > xlog_valid_rec_header( > struct xlog *log, > struct xlog_rec_header *rhead, > - xfs_daddr_t blkno) > + xfs_daddr_t blkno, > + int bufsize) > { > int hlen; > > @@ -2894,10 +2895,14 @@ xlog_valid_rec_header( > return -EFSCORRUPTED; > } > > - /* LR body must have data or it wouldn't have been written */ > + /* > + * LR body must have data (or it wouldn't have been written) > + * and h_len must not be greater than LR buffer size. > + */ > hlen = be32_to_cpu(rhead->h_len); > - if (XFS_IS_CORRUPT(log->l_mp, hlen <= 0 || hlen > INT_MAX)) > + if (XFS_IS_CORRUPT(log->l_mp, hlen <= 0 || hlen > bufsize)) > return -EFSCORRUPTED; > + > if (XFS_IS_CORRUPT(log->l_mp, > blkno > log->l_logBBsize || blkno > INT_MAX)) > return -EFSCORRUPTED; > @@ -2958,9 +2963,6 @@ xlog_do_recovery_pass( > goto bread_err1; > > rhead = (xlog_rec_header_t *)offset; > - error = xlog_valid_rec_header(log, rhead, tail_blk); > - if (error) > - goto bread_err1; > > /* > * xfsprogs has a bug where record length is based on lsunit but > @@ -2975,21 +2977,18 @@ xlog_do_recovery_pass( > */ > h_size = be32_to_cpu(rhead->h_size); > h_len = be32_to_cpu(rhead->h_len); > - if (h_len > h_size) { > - if (h_len <= log->l_mp->m_logbsize && > - be32_to_cpu(rhead->h_num_logops) == 1) { > - xfs_warn(log->l_mp, > + if (h_len > h_size && h_len <= log->l_mp->m_logbsize && > + rhead->h_num_logops == cpu_to_be32(1)) { > + xfs_warn(log->l_mp, > "invalid iclog size (%d bytes), using lsunit (%d bytes)", > - h_size, log->l_mp->m_logbsize); > - h_size = log->l_mp->m_logbsize; > - } else { > - XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_LOW, > - log->l_mp); > - error = -EFSCORRUPTED; > - goto bread_err1; > - } > + h_size, log->l_mp->m_logbsize); > + h_size = log->l_mp->m_logbsize; > } > > + error = xlog_valid_rec_header(log, rhead, tail_blk, h_size); > + if (error) > + goto bread_err1; > + > if ((be32_to_cpu(rhead->h_version) & XLOG_VERSION_2) && > (h_size > XLOG_HEADER_CYCLE_SIZE)) { > hblks = h_size / XLOG_HEADER_CYCLE_SIZE; > @@ -3070,7 +3069,7 @@ xlog_do_recovery_pass( > } > rhead = (xlog_rec_header_t *)offset; > error = xlog_valid_rec_header(log, rhead, > - split_hblks ? blk_no : 0); > + split_hblks ? blk_no : 0, h_size); > if (error) > goto bread_err2; > > @@ -3151,7 +3150,7 @@ xlog_do_recovery_pass( > goto bread_err2; > > rhead = (xlog_rec_header_t *)offset; > - error = xlog_valid_rec_header(log, rhead, blk_no); > + error = xlog_valid_rec_header(log, rhead, blk_no, h_size); > if (error) > goto bread_err2; > > -- > 2.18.1 >
On Wed, Sep 23, 2020 at 09:35:40AM -0700, Darrick J. Wong wrote: > On Thu, Sep 17, 2020 at 01:13:40PM +0800, Gao Xiang wrote: > > Currently, crafted h_len has been blocked for the log > > header of the tail block in commit a70f9fe52daa ("xfs: > > detect and handle invalid iclog size set by mkfs"). > > > > However, each log record could still have crafted h_len > > and cause log record buffer overrun. So let's check > > h_len vs buffer size for each log record as well. > > > > Signed-off-by: Gao Xiang <hsiangkao@redhat.com> > > /me squints real hard and thinks he understands what this patch does. > > Tighten up xlog_valid_rec_header, and add a new callsite in the middle > of xlog_do_recovery_pass instead of the insufficient length checking. > Assuming that's right, > > Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Thanks for the review! The main point is to check each individual LR h_len against LR buffer size allocated first in xlog_do_recovery_pass() to avoid buffer overflow triggered by CRC calc or follow-up steps (details in https://lore.kernel.org/linux-xfs/20200902224726.GB4671@xiangao.remote.csb/ ). no new callsite (just move the callsite after original workaround code). Anyway, that is just a buffer overflow issue can be triggered by corrupted log. Just a minor stuff but security guyes could also keep eyes on such thing. I think that is right. :) Thanks, Gao Xiang > > --D
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c index a17d788921d6..782ec3eeab4d 100644 --- a/fs/xfs/xfs_log_recover.c +++ b/fs/xfs/xfs_log_recover.c @@ -2878,7 +2878,8 @@ STATIC int xlog_valid_rec_header( struct xlog *log, struct xlog_rec_header *rhead, - xfs_daddr_t blkno) + xfs_daddr_t blkno, + int bufsize) { int hlen; @@ -2894,10 +2895,14 @@ xlog_valid_rec_header( return -EFSCORRUPTED; } - /* LR body must have data or it wouldn't have been written */ + /* + * LR body must have data (or it wouldn't have been written) + * and h_len must not be greater than LR buffer size. + */ hlen = be32_to_cpu(rhead->h_len); - if (XFS_IS_CORRUPT(log->l_mp, hlen <= 0 || hlen > INT_MAX)) + if (XFS_IS_CORRUPT(log->l_mp, hlen <= 0 || hlen > bufsize)) return -EFSCORRUPTED; + if (XFS_IS_CORRUPT(log->l_mp, blkno > log->l_logBBsize || blkno > INT_MAX)) return -EFSCORRUPTED; @@ -2958,9 +2963,6 @@ xlog_do_recovery_pass( goto bread_err1; rhead = (xlog_rec_header_t *)offset; - error = xlog_valid_rec_header(log, rhead, tail_blk); - if (error) - goto bread_err1; /* * xfsprogs has a bug where record length is based on lsunit but @@ -2975,21 +2977,18 @@ xlog_do_recovery_pass( */ h_size = be32_to_cpu(rhead->h_size); h_len = be32_to_cpu(rhead->h_len); - if (h_len > h_size) { - if (h_len <= log->l_mp->m_logbsize && - be32_to_cpu(rhead->h_num_logops) == 1) { - xfs_warn(log->l_mp, + if (h_len > h_size && h_len <= log->l_mp->m_logbsize && + rhead->h_num_logops == cpu_to_be32(1)) { + xfs_warn(log->l_mp, "invalid iclog size (%d bytes), using lsunit (%d bytes)", - h_size, log->l_mp->m_logbsize); - h_size = log->l_mp->m_logbsize; - } else { - XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_LOW, - log->l_mp); - error = -EFSCORRUPTED; - goto bread_err1; - } + h_size, log->l_mp->m_logbsize); + h_size = log->l_mp->m_logbsize; } + error = xlog_valid_rec_header(log, rhead, tail_blk, h_size); + if (error) + goto bread_err1; + if ((be32_to_cpu(rhead->h_version) & XLOG_VERSION_2) && (h_size > XLOG_HEADER_CYCLE_SIZE)) { hblks = h_size / XLOG_HEADER_CYCLE_SIZE; @@ -3070,7 +3069,7 @@ xlog_do_recovery_pass( } rhead = (xlog_rec_header_t *)offset; error = xlog_valid_rec_header(log, rhead, - split_hblks ? blk_no : 0); + split_hblks ? blk_no : 0, h_size); if (error) goto bread_err2; @@ -3151,7 +3150,7 @@ xlog_do_recovery_pass( goto bread_err2; rhead = (xlog_rec_header_t *)offset; - error = xlog_valid_rec_header(log, rhead, blk_no); + error = xlog_valid_rec_header(log, rhead, blk_no, h_size); if (error) goto bread_err2;
Currently, crafted h_len has been blocked for the log header of the tail block in commit a70f9fe52daa ("xfs: detect and handle invalid iclog size set by mkfs"). However, each log record could still have crafted h_len and cause log record buffer overrun. So let's check h_len vs buffer size for each log record as well. Signed-off-by: Gao Xiang <hsiangkao@redhat.com> --- v3: https://lore.kernel.org/r/20200904082516.31205-2-hsiangkao@redhat.com changes since v3: - drop exception comment to avoid confusion (Brian); - check rhead->hlen vs buffer size to address the harmful overflow (Brian); And as Brian requested previously, "Also, please test the workaround case to make sure it still works as expected (if you haven't already)." So I tested the vanilla/after upstream kernels with compiled xfsprogs-v4.3.0, which was before mkfs fix 20fbd4593ff2 ("libxfs: format the log with valid log record headers") got merged, and I generated a questionable image followed by the instruction described in the related commit messages with "mkfs.xfs -dsunit=512,swidth=4096 -f test.img" and logprint says cycle: 1 version: 2 lsn: 1,0 tail_lsn: 1,0 length of Log Record: 261632 prev offset: -1 num ops: 1 uuid: 7b84cd80-7855-4dc8-91ce-542c7d65ba99 format: little endian linux h_size: 32768 so "length of Log Record" is overrun obviously, but I cannot reproduce the described workaround case for vanilla/after kernels anymore. I think the reason is due to commit 7f6aff3a29b0 ("xfs: only run torn log write detection on dirty logs"), which changes the behavior described in commit a70f9fe52daa8 ("xfs: detect and handle invalid iclog size set by mkfs") from "all records at the head of the log are verified for CRC errors" to "we can only run CRC verification when the log is dirty because there's no guarantee that the log data behind an unmount record is compatible with the current architecture).", more details see codediff of a70f9fe52daa8. The timeline seems to be: https://lore.kernel.org/r/1447342648-40012-1-git-send-email-bfoster@redhat.com a70f9fe52daa [PATCH v2 1/8] xfs: detect and handle invalid iclog size set by mkfs 7088c4136fa1 [PATCH v2 7/8] xfs: detect and trim torn writes during log recovery https://lore.kernel.org/r/1457008798-58734-5-git-send-email-bfoster@redhat.com 7f6aff3a29b0 [PATCH 4/4] xfs: only run torn log write detection on dirty logs so IMHO, the workaround a70f9fe52daa would only be useful between 7088c4136fa1 ~ 7f6aff3a29b0. Yeah, it relates to several old kernel commits/versions, my technical analysis is as above. This patch doesn't actually change the real original workaround logic. Even if the workground can be removed now, that should be addressed with another patch and that is quite another story. Kindly correct me if I'm wrong :-) Thanks, Gao Xiang fs/xfs/xfs_log_recover.c | 39 +++++++++++++++++++-------------------- 1 file changed, 19 insertions(+), 20 deletions(-)