The CI this week reports a new test failure of the tests/basenc/basenc test,
when compiled with sanitizers.
How to reproduce:
1. Build the current coreutils with
CC="clang
-fsanitize=address,undefined,signed-integer-overflow,shift,integer-divide-by-zero
-fno-sanitize-recover=undefined"
configuring it with option --without-libgmp . (There is no issue when
coreutils uses the real gmp.)
2.
$ src/basenc --base58 < /dev/null
../lib/mini-gmp.c:4529:9: runtime error: applying non-zero offset
18446744073709551615 to null pointer
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior
../lib/mini-gmp.c:4529:9
Aborted
gdb stack trace:
#7 0x0000555555696e79 in __ubsan_handle_pointer_overflow_abort ()
at
/home/runner/work/llvm-project/llvm-project/compiler-rt/lib/ubsan/ubsan_handlers.cpp:855
#8 0x00005555556e27a2 in mpz_import (r=0x7bfff5900060, count=0, order=1,
size=1, endian=-1, nails=0, src=0x0) at ../lib/mini-gmp.c:4529
#9 0x00005555556a70a7 in base58_encode (data=0x0, data_len=0,
out=0x7edff6de0400 '\276' <repeats 200 times>..., outlen=0x7bfff5b000c0)
at ../src/basenc.c:1178
#10 0x00005555556a2d56 in base58_encode_ctx_finalize (ctx=0x7bfff5b00060,
out=0x7bfff5b00040, outlen=0x7bfff5b000c0)
at ../src/basenc.c:1200
#11 0x00005555556a65d1 in do_encode (in=0x7ffff7e038e0 <_IO_2_1_stdin_>,
infile=0x55555570fd60 <str> "-",
out=0x7ffff7e045c0 <_IO_2_1_stdout_>, wrap_column=76) at
../src/basenc.c:1431
#12 0x0000555555699973 in main (argc=2, argv=0x7fffffffcfd8) at
../src/basenc.c:1736
Adding a non-zero offset to a NULL pointer is undefined behaviour per
ISO C 23 ยง 6.5.7.(9) as amended by N3322.
Should mpz_import accept count=0, src=NULL arguments? Hard to say from the gmp
documentation https://gmplib.org/manual/Integer-Import-and-Export .
If yes, then it's a bug in mini-gmp.c around line 4529.
If no, it's a bug in coreutils/src/basenc.c.
If yes, feel free to report that to the GMP people, without CCing me, please.
If no, feel free to apply the attached fix. It passes "make check".
Bruno
>From 1d5042677fc8be29aa95451db2cd23b9ab3a32a8 Mon Sep 17 00:00:00 2001
From: Bruno Haible <br...@clisp.org>
Date: Tue, 12 Aug 2025 02:25:41 +0200
Subject: [PATCH] basenc: Don't trigger undefined behaviour in mini-gmp
* src/basenc.c (base58_encode): Avoid calling mpz_import on an empty
limb sequence.
---
src/basenc.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/src/basenc.c b/src/basenc.c
index dbe3b388f..84789e2de 100644
--- a/src/basenc.c
+++ b/src/basenc.c
@@ -1175,10 +1175,12 @@ base58_encode (char const* data, size_t data_len,
/* Use GMP to convert from base 256 to base 58. */
mpz_t num;
mpz_init (num);
- mpz_import (num, data_len - zeros, 1, 1, 0, 0, data + zeros);
if (data_len - zeros)
- for (p = mpz_get_str (p, 58, num); *p; p++)
- *p = gmp_to_base58[to_uchar (*p)];
+ {
+ mpz_import (num, data_len - zeros, 1, 1, 0, 0, data + zeros);
+ for (p = mpz_get_str (p, 58, num); *p; p++)
+ *p = gmp_to_base58[to_uchar (*p)];
+ }
mpz_clear (num);
*outlen = p - out;
--
2.50.1
