Security advisory for musl libc - stack-based buffer overflow in ipv6 literal parsing [CVE-2015-1817]

[Rich Felker <dalias@libc.org>]

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A stack-based buffer overflow has been found in musl libc's ipv6
address literal parsing code. Programs which call the inet_pton or
getaddrinfo function with AF_INET6 or AF_UNSPEC and untrusted address
strings are affected. Successful exploitation yields control of the
return address. Having enabled stack protector at the application
level does not mitigate the issue. All users should patch or upgrade.

Software: musl libc (http://www.musl-libc.org)

Severity: high

Affected Versions: 0.9.15 - 1.0.4, 1.1.0 - 1.1.7.

Bug introduced in commit: 78f889153167452de4cbced921f6428b3d4f663a

Bug fixed in commit: fc13acc3dcb5b1f215c007f583a63551f6a71363

Patch: musl_dn_expand_overflow_fix.diff (attached) (fix+hardening)

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diff --git a/src/network/inet_pton.c b/src/network/inet_pton.c
index 4496b47..d36c368 100644
--- a/src/network/inet_pton.c
+++ b/src/network/inet_pton.c
@@ -39,14 +39,15 @@ int inet_pton(int af, const char *restrict s, void *restrict a0)
 	for (i=0; ; i++) {
 		if (s[0]==':' && brk<0) {
 			brk=i;
-			ip[i]=0;
+			ip[i&7]=0;
 			if (!*++s) break;
+			if (i==7) return 0;
 			continue;
 		}
 		for (v=j=0; j<4 && (d=hexval(s[j]))>=0; j++)
 			v=16*v+d;
 		if (j==0) return 0;
-		ip[i] = v;
+		ip[i&7] = v;
 		if (!s[j] && (brk>=0 || i==7)) break;
 		if (i==7) return 0;
 		if (s[j]!=':') {