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Second thoughts on TOAST decompression.
Mon, 2 Nov 2020 16:25:18 +0000 (11:25 -0500)
Mon, 2 Nov 2020 16:25:18 +0000 (11:25 -0500)
On detecting a corrupted match tag, pglz_decompress() should just
summarily return -1. Breaking out of the loop, as I did in dfc797730,
doesn't quite guarantee that will happen. Also, we can use
unlikely() on that check, just in case it helps.

Backpatch to v13, like the previous patch.


diff --git a/src/common/pg_lzcompress.c b/src/common/pg_lzcompress.c
index 79747767ce08a0144b85d3496d8def6b74071825..f9c29820e30bd584d7ec4636a6043b0864a30318 100644 (file)
--- a/src/common/pg_lzcompress.c
+++ b/src/common/pg_lzcompress.c
@@ -680,9 +680,12 @@ pglz_compress(const char *source, int32 slen, char *dest,
* pglz_decompress -
*
* Decompresses source into dest. Returns the number of bytes
- * decompressed in the destination buffer, and *optionally*
- * checks that both the source and dest buffers have been
- * fully read and written to, respectively.
+ * decompressed into the destination buffer, or -1 if the
+ * compressed data is corrupted.
+ *
+ * If check_complete is true, the data is considered corrupted
+ * if we don't exactly fill the destination buffer. Callers that
+ * are extracting a slice typically can't apply this check.
* ----------
*/
int32
@@ -736,8 +739,8 @@ pglz_decompress(const char *source, int32 slen, char *dest,
* must check this, else we risk an infinite loop below in the
* face of corrupt data.)
*/
- if (sp > srcend || off == 0)
- break;
+ if (unlikely(sp > srcend || off == 0))
+ return -1;
/*
* Don't emit more data than requested.
@@ -809,9 +812,7 @@ pglz_decompress(const char *source, int32 slen, char *dest,
}
/*
- * Check we decompressed the right amount. If we are slicing, then we
- * won't necessarily be at the end of the source or dest buffers when we
- * hit a stop, so we don't test them.
+ * If requested, check we decompressed the right amount.
*/
if (check_complete && (dp != destend || sp != srcend))
return -1;
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