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commit    2efca163399ba1be4c2991635960ed509f6e7cfd
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Sun Oct 19 18:36:58 2025 +0000
First released in: 13.23, 14.20, 15.15, 16.11, 17.7, 18.1

    Don't rely on zlib's gzgetc() macro.
    
    It emerges that zlib's configuration logic is not robust enough
    to guarantee that the macro will have the same ideas about struct
    field layout as the library itself does, leading to corruption of
    zlib's state struct followed by unintelligible failure messages.
    This hazard has existed for a long time, but we'd not noticed
    for several reasons:
    
    (1) We only use gzgetc() when trying to read a manually-compressed
    TOC file within a directory-format dump, which is a rarely-used
    scenario that we weren't even testing before 20ec99589.
    
    (2) No corruption actually occurs unless sizeof(long) is different
    from sizeof(off_t) and the platform is big-endian.
    
    (3) Some platforms have already fixed the configuration instability,
    at least sufficiently for their environments.
    
    Despite (3), it seems foolish to assume that the problem isn't
    going to be present in some environments for a long time to come.
    Hence, avoid relying on this macro.  We can just #undef it and
    fall back on the underlying function of the same name.
    
    Author: Tom Lane <tgl@sss.pgh.pa.us>
    Discussion: https://postgr.es/m/2122679.1760846783@sss.pgh.pa.us
    Backpatch-through: 13


 src/bin/pg_dump/compress_gzip.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/bin/pg_dump/compress_gzip.c b/src/bin/pg_dump/compress_gzip.c
index 85b5da3790f..c327ba38439 100644
--- a/src/bin/pg_dump/compress_gzip.c
+++ b/src/bin/pg_dump/compress_gzip.c
@@ -20,6 +20,15 @@
 #ifdef HAVE_LIBZ
 #include "zlib.h"
 
+/*
+ * We don't use the gzgetc() macro, because zlib's configuration logic is not
+ * robust enough to guarantee that the macro will have the same ideas about
+ * struct field layout as the library itself does; see for example
+ * https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=59711
+ * Instead, #undef the macro and fall back to the underlying function.
+ */
+#undef gzgetc
+
 /*----------------------
  * Compressor API
  *----------------------


[parent: d4e8c37cca39]