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From 63cee29a64ac6a02695a91f7a8f29ac0c17ef3f0 Mon Sep 17 00:00:00 2001
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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Tue, 26 Feb 2019 14:44:14 +0000
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Subject: [PATCH] scsi-generic: avoid possible out-of-bounds access to r->buf
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RH-Author: Paolo Bonzini <pbonzini@redhat.com>
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Message-id: <20190226144414.5700-1-pbonzini@redhat.com>
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Patchwork-id: 84717
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O-Subject: [RHEL8.0 qemu-kvm PATCH] scsi-generic: avoid possible out-of-bounds access to r->buf
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Bugzilla: 1668162
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RH-Acked-by: Thomas Huth <thuth@redhat.com>
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RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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Bugzilla: 1668162
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Brew build: 20372796
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Whenever the allocation length of a SCSI request is shorter than the size of the
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VPD page list, page_idx is used blindly to index into r->buf.  Even though
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the stores in the insertion sort are protected against overflows, the same is not
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true of the reads and the final store of 0xb0.
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This basically does the same thing as commit 57dbb58d80 ("scsi-generic: avoid
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out-of-bounds access to VPD page list", 2018-11-06), except that here the
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allocation length can be chosen by the guest.  Note that according to the SCSI
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standard, the contents of the PAGE LENGTH field are not altered based
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on the allocation length.
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The code was introduced by commit 6c219fc8a1 ("scsi-generic: keep VPD
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page list sorted", 2018-11-06) but the overflow was already possible before.
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Reported-by: Kevin Wolf <kwolf@redhat.com>
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Fixes: a71c775b24ebc664129eb1d9b4c360590353efd5
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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(cherry picked from commit e909ff93698851777faac3c45d03c1b73f311ea6)
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Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
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---
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 hw/scsi/scsi-generic.c | 18 ++++++++++--------
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 1 file changed, 10 insertions(+), 8 deletions(-)
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diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
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index 4ac53e4..e21adf9 100644
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--- a/hw/scsi/scsi-generic.c
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+++ b/hw/scsi/scsi-generic.c
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@@ -183,7 +183,7 @@ static void scsi_handle_inquiry_reply(SCSIGenericReq *r, SCSIDevice *s)
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             /* Also take care of the opt xfer len. */
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             stl_be_p(&r->buf[12],
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                     MIN_NON_ZERO(max_transfer, ldl_be_p(&r->buf[12])));
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-        } else if (s->needs_vpd_bl_emulation && page == 0x00) {
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+        } else if (s->needs_vpd_bl_emulation && page == 0x00 && r->buflen >= 4) {
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             /*
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              * Now we're capable of supplying the VPD Block Limits
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              * response if the hardware can't. Add it in the INQUIRY
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@@ -194,18 +194,20 @@ static void scsi_handle_inquiry_reply(SCSIGenericReq *r, SCSIDevice *s)
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              * and will use it to proper setup the SCSI device.
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              *
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              * VPD page numbers must be sorted, so insert 0xb0 at the
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-             * right place with an in-place insert.  After the initialization
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-             * part of the for loop is executed, the device response is
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-             * at r[0] to r[page_idx - 1].
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+             * right place with an in-place insert.  When the while loop
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+             * begins the device response is at r[0] to r[page_idx - 1].
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              */
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-            for (page_idx = lduw_be_p(r->buf + 2) + 4;
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-                 page_idx > 4 && r->buf[page_idx - 1] >= 0xb0;
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-                 page_idx--) {
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+            page_idx = lduw_be_p(r->buf + 2) + 4;
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+            page_idx = MIN(page_idx, r->buflen);
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+            while (page_idx > 4 && r->buf[page_idx - 1] >= 0xb0) {
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                 if (page_idx < r->buflen) {
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                     r->buf[page_idx] = r->buf[page_idx - 1];
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                 }
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+                page_idx--;
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+            }
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+            if (page_idx < r->buflen) {
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+                r->buf[page_idx] = 0xb0;
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             }
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-            r->buf[page_idx] = 0xb0;
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             stw_be_p(r->buf + 2, lduw_be_p(r->buf + 2) + 1);
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         }
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     }
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-- 
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1.8.3.1
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