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authorMartin K. Petersen2022-03-02 00:35:47 -0500
committerMartin K. Petersen2022-05-02 16:59:10 -0400
commitc92a6b5d63359dd6d2ce6ea88ecd8e31dd769f6b (patch)
tree00a7cbfb41e6244490e91f0cc5c7c15d9461fc11 /CREDITS
parentdc1178767cba9d67f5100fb370670fd613319362 (diff)
scsi: core: Query VPD size before getting full page
We currently default to 255 bytes when fetching VPD pages during discovery. However, we have had a few devices that are known to wedge if the requested buffer exceeds a certain size. See commit af73623f5f10 ("[SCSI] sd: Reduce buffer size for vpd request") which works around one example of this problem in the SCSI disk driver. With commit d188b0675b21 ("scsi: core: Add sysfs attributes for VPD pages 0h and 89h") we now risk triggering the same issue in the generic midlayer code. The problem with the ATA VPD page in particular is that the SCSI portion of the page is trailed by 512 bytes of verbatim ATA Identify Device information. However, not all controllers actually provide the additional 512 bytes and will lock up if one asks for more than the 64 bytes containing the SCSI protocol fields. Instead of picking a new, somewhat arbitrary, number of bytes for the VPD buffer size, start fetching the 4-byte header for each page. The header contains the size of the page as far as the device is concerned. We can use the reported size to specify the correct allocation length when subsequently fetching the full page. The header validation is done by a new helper function scsi_get_vpd_size() and both scsi_get_vpd_page() and scsi_get_vpd_buf() now rely on this to query the page size. In addition, scsi_get_vpd_page() is simplified to mirror the logic in scsi_get_vpd_page(). This involves removing the Supported VPD Pages lookup prior to attempting to query a page. There does not appear any evidence, even in the oldest SCSI specs, that this step is required. We already rely on scsi_get_vpd_page() throughout the stack and this function never consulted the Supported VPD Pages. Since this has not caused any problems it should be safe to remove the precondition from scsi_get_vpd_page(). Instrumented runs also revealed that the Supported VPD Pages lookup had little effect since the device page index often was larger than the supplied buffer size. As a result, inquiries frequently bypassed the index check and went through the "If we ran off the end of the buffer, give us the benefit of the doubt" code path which assumed the page was present despite not being listed. The revised code takes both the page size reported by the device as well as the size of the buffer provided by the scsi_get_vpd_page() caller into account. Link: https://lore.kernel.org/r/20220302053559.32147-3-martin.petersen@oracle.com Fixes: d188b0675b21 ("scsi: core: Add sysfs attributes for VPD pages 0h and 89h") Reported-by: Maciej W. Rozycki <macro@orcam.me.uk> Tested-by: Maciej W. Rozycki <macro@orcam.me.uk> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
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