Fix a crash when attempting to read a block pointer with no valid DVAs #17078
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asomers
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amotin
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Feb 20, 2025
amotin
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Feb 21, 2025
amotin
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Feb 21, 2025
behlendorf
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Feb 25, 2025
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@asomers Could you look on the remaining comment? |
alek-p
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Feb 26, 2025
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@amotin are there any other questions you have for me? |
@asomers I closed one conversation for later, but another one is still not answered -- added comment there. And Github wants a rebase. |
amotin
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Mar 12, 2025
Now instead of crashing when attempting to read the corrupt block pointer, ZFS will return ECKSUM, in a stack that looks like this: ``` none:set-error zfs.ko`arc_read+0x1d82 zfs.ko`dbuf_read+0xa8c zfs.ko`dmu_buf_hold_array_by_dnode+0x292 zfs.ko`dmu_read_uio_dnode+0x47 zfs.ko`zfs_read+0x2d5 zfs.ko`zfs_freebsd_read+0x7b kernel`VOP_READ_APV+0xd0 kernel`vn_read+0x20e kernel`vn_io_fault_doio+0x45 kernel`vn_io_fault1+0x15e kernel`vn_io_fault+0x150 kernel`dofileread+0x80 kernel`sys_read+0xb7 kernel`amd64_syscall+0x424 kernel`0xffffffff810633cb ``` This patch should hopefully also prevent such corrupt block pointers from being written to disk in the first place. And in zdb, don't crash when printing a block pointer with no valid DVAs. If a block pointer isn't embedded yet doesn't have any valid DVAs, that's a data corruption bug. zdb should be able to handle the situation gracefully. Finally, remove an extra check for gang blocks in SNPRINTF_BLKPTR. This check, which compares the asizes of two different DVAs within the same BP, was added by illumos-gate commit b24ab67[^1], and I can't understand why. It doesn't appear to do anything useful, so remove it. Fixes openzfs#17077 Sponsored by: ConnectWise Signed-off-by: Alan Somers <[email protected]> [^1]: illumos/illumos-gate@b24ab67
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Motivation and Context
Somehow ZFS wrote to my pool a block pointer that is neither embedded nor a hole, yet contains no DVAs with a non-zero asize. That should be impossible, but it happened. This PR will cause ZFS to return
ECKSUMwhen attempting to read from that block pointer, rather than crashing. This PR will also fix zdb so it can display such block pointers. Finally, I believe that this PR will prevent such block pointers from being written to disk in the first place, by triggering a panic inzfs_blkptr_verifyin the write path.Description
zfs_blkptr_verifyto ensure that every block pointer is either embedded, hole, or has at least one valid DVA.How Has This Been Tested?
Tested on FreeBSD 15.0-CURRENT by trying to read from a suitably corrupted dataset.
Types of changes
Checklist:
Signed-off-by.