From f1c16e6c37b1c74ac2c2cb94bc82ae1f56c04acd Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Thu, 23 Mar 2023 14:02:35 -0400 Subject: [PATCH 1/2] amcheck: Tighten up validation of redirect line pointers. Commit bbc1376b39627c6bddd8a0dc0a7dda24c91a97a0 added a new lp_valid[] array which records whether or not a line pointer was thought to be valid, but entries could sometimes get set to true in cases where that wasn't actually safe. Fix that. Suppose A is a redirect line pointer and B is the other line pointer to which it points. The old code could mishandle this situation in a couple of different ways. First, if B was unused, we'd complain about corruption but still set lp_valid[A] = true, causing later code to try to access the B as if it were pointing to a tuple. Second, if B was dead, we wouldn't complain about corruption at all, which is an oversight, and would also set lp_valid[A] = true, which would again confuse later code. Fix all that. In the case where B is a redirect, the old code was correct, but refactor things a bit anyway so that all of these cases are handled more symmetrically. Also add an Assert() and some comments. Andres Freund and Robert Haas --- contrib/amcheck/verify_heapam.c | 40 +++++++++++++++++++++++++-------- 1 file changed, 31 insertions(+), 9 deletions(-) diff --git a/contrib/amcheck/verify_heapam.c b/contrib/amcheck/verify_heapam.c index 1b8607c6cc..487bc25de5 100644 --- a/contrib/amcheck/verify_heapam.c +++ b/contrib/amcheck/verify_heapam.c @@ -481,11 +481,35 @@ verify_heapam(PG_FUNCTION_ARGS) (unsigned) maxoff)); continue; } + + /* + * Since we've checked that this redirect points to a line + * pointer between FirstOffsetNumber and maxoff, it should + * now be safe to fetch the referenced line pointer. We expect + * it to be LP_NORMAL; if not, that's corruption. + */ rditem = PageGetItemId(ctx.page, rdoffnum); if (!ItemIdIsUsed(rditem)) + { report_corruption(&ctx, - psprintf("line pointer redirection to unused item at offset %u", + psprintf("redirected line pointer points to an unused item at offset %u", (unsigned) rdoffnum)); + continue; + } + else if (ItemIdIsDead(rditem)) + { + report_corruption(&ctx, + psprintf("redirected line pointer points to a dead item at offset %u", + (unsigned) rdoffnum)); + continue; + } + else if (ItemIdIsRedirected(rditem)) + { + report_corruption(&ctx, + psprintf("redirected line pointer points to another redirected line pointer at offset %u", + (unsigned) rdoffnum)); + continue; + } /* * Record the fact that this line pointer has passed basic @@ -584,14 +608,12 @@ verify_heapam(PG_FUNCTION_ARGS) /* Handle the cases where the current line pointer is a redirect. */ if (ItemIdIsRedirected(curr_lp)) { - /* Can't redirect to another redirect. */ - if (ItemIdIsRedirected(next_lp)) - { - report_corruption(&ctx, - psprintf("redirected line pointer points to another redirected line pointer at offset %u", - (unsigned) nextoffnum)); - continue; - } + /* + * We should not have set successor[ctx.offnum] to a value + * other than InvalidOffsetNumber unless that line pointer + * is LP_NORMAL. + */ + Assert(ItemIdIsNormal(next_lp)); /* Can only redirect to a HOT tuple. */ next_htup = (HeapTupleHeader) PageGetItem(ctx.page, next_lp); -- 2.37.1 (Apple Git-137.1)