fix: patch musl to mitigate CVE-2025-26519

Ref: https://www.openwall.com/lists/musl/2025/02/13/1

Also ensure usr and sbin merge in the final image

Signed-off-by: Dmitry Sharshakov <dmitry.sharshakov@siderolabs.com>

Author: dsseng

toolchain-musl/patches/0001-iconv-fix-erroneous-input-validation-in-EUC-KR-decod.patch

@@ -0,0 +1,38 @@
+>From e5adcd97b5196e29991b524237381a0202a60659 Mon Sep 17 00:00:00 2001
+From: Rich Felker <dalias@aerifal.cx>
+Date: Sun, 9 Feb 2025 10:07:19 -0500
+Subject: [PATCH] iconv: fix erroneous input validation in EUC-KR decoder
+
+as a result of incorrect bounds checking on the lead byte being
+decoded, certain invalid inputs which should produce an encoding
+error, such as "\xc8\x41", instead produced out-of-bounds loads from
+the ksc table.
+
+in a worst case, the loaded value may not be a valid unicode scalar
+value, in which case, if the output encoding was UTF-8, wctomb would
+return (size_t)-1, causing an overflow in the output pointer and
+remaining buffer size which could clobber memory outside of the output
+buffer.
+
+bug report was submitted in private by Nick Wellnhofer on account of
+potential security implications.
+---
+ src/locale/iconv.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/src/locale/iconv.c b/src/locale/iconv.c
+index 9605c8e9..008c93f0 100644
+--- a/src/locale/iconv.c
++++ b/src/locale/iconv.c
+@@ -502,7 +502,7 @@ size_t iconv(iconv_t cd, char **restrict in, size_t *restrict inb, char **restri
+ 			if (c >= 93 || d >= 94) {
+ 				c += (0xa1-0x81);
+ 				d += 0xa1;
+-				if (c >= 93 || c>=0xc6-0x81 && d>0x52)
++				if (c > 0xc6-0x81 || c==0xc6-0x81 && d>0x52)
+ 					goto ilseq;
+ 				if (d-'A'<26) d = d-'A';
+ 				else if (d-'a'<26) d = d-'a'+26;
+-- 
+2.21.0
+

toolchain-musl/patches/0002-iconv-harden-UTF-8-output-code-path-against-input-de.patch

@@ -0,0 +1,38 @@
+>From c47ad25ea3b484e10326f933e927c0bc8cded3da Mon Sep 17 00:00:00 2001
+From: Rich Felker <dalias@aerifal.cx>
+Date: Wed, 12 Feb 2025 17:06:30 -0500
+Subject: [PATCH] iconv: harden UTF-8 output code path against input decoder
+ bugs
+
+the UTF-8 output code was written assuming an invariant that iconv's
+decoders only emit valid Unicode Scalar Values which wctomb can encode
+successfully, thereby always returning a value between 1 and 4.
+
+if this invariant is not satisfied, wctomb returns (size_t)-1, and the
+subsequent adjustments to the output buffer pointer and remaining
+output byte count overflow, moving the output position backwards,
+potentially past the beginning of the buffer, without storing any
+bytes.
+---
+ src/locale/iconv.c | 4 ++++
+ 1 file changed, 4 insertions(+)
+
+diff --git a/src/locale/iconv.c b/src/locale/iconv.c
+index 008c93f0..52178950 100644
+--- a/src/locale/iconv.c
++++ b/src/locale/iconv.c
+@@ -545,6 +545,10 @@ size_t iconv(iconv_t cd, char **restrict in, size_t *restrict inb, char **restri
+ 				if (*outb < k) goto toobig;
+ 				memcpy(*out, tmp, k);
+ 			} else k = wctomb_utf8(*out, c);
++			/* This failure condition should be unreachable, but
++			 * is included to prevent decoder bugs from translating
++			 * into advancement outside the output buffer range. */
++			if (k>4) goto ilseq;
+ 			*out += k;
+ 			*outb -= k;
+ 			break;
+-- 
+2.21.0
+
+

toolchain-musl/pkg.yaml

@@ -20,6 +20,8 @@ steps:
 
         patch -p1 < /pkg/patches/handle-aux-at-base.patch
         patch -p1 < /pkg/patches/close-range.patch
+        patch -p1 < /pkg/patches/0001-iconv-fix-erroneous-input-validation-in-EUC-KR-decod.patch
+        patch -p1 < /pkg/patches/0002-iconv-harden-UTF-8-output-code-path-against-input-de.patch
 
         mkdir build
         cd build

toolchain/pkg.yaml

@@ -9,6 +9,24 @@ dependencies:
   - stage: make
   - stage: golang
 steps:
+  - build:
+    - |
+      # Check usrmerge symlinks are in place and point to directories
+      mkdir -p /usr/bin /usr/lib
+      [ -L /bin ] && [ -d /bin ]
+      [ -L /lib ] && [ -d /lib ]
+      [ -L /lib64 ] && [ -d /lib64 ]
+      [ -L /usr/lib64 ] && [ -d /usr/lib64 ]
+    - |
+      # Ensure sbin either doesn't exist or is empty, so we don't lose any executables
+      [ ! -e /sbin ] || [ -z "$(ls -A /sbin 2>/dev/null)" ]
+      [ ! -e /usr/sbin ] || [ -z "$(ls -A /usr/sbin 2>/dev/null)" ]
+      rm -rf /sbin
+      rm -rf /usr/sbin
+    - |
+      # /usr/sbin -> /usr/bin
+      ln -sT usr/bin /sbin
+      ln -sT bin /usr/sbin
   - test:
     - |
       echo 'int main(){}' > dummy.c