[PATCH] fix ldso reserved library name handling

[PATCH] fix ldso reserved library name handling

[Szabolcs Nagy]

If a DT_NEEDED entry was the prefix of a reserved library name
(up to the first dot) then it was incorrectly treated as a libc
reserved name.

e.g. libp.so dependency was not loaded as it matched libpthread
reserved name.
---

this is not the smallest possible patch (most of the diff is
indentation change), but i found the code cleaner without
the z and l-3 computation.

 ldso/dynlink.c | 38 +++++++++++++++++++-------------------
 1 file changed, 19 insertions(+), 19 deletions(-)

diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index d11776d..acb73bc 100644
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -906,27 +906,27 @@ static struct dso *load_library(const char *name, struct dso *needed_by)
 	/* Catch and block attempts to reload the implementation itself */
 	if (name[0]=='l' && name[1]=='i' && name[2]=='b') {
 		static const char reserved[] =
-			"c\0pthread\0rt\0m\0dl\0util\0xnet\0";
-		const char *rp;
-		char *z = strchr(name, '.');
-		if (z) {
-			size_t l = z-name;
-			for (rp=reserved; *rp && strncmp(name+3, rp, l-3); rp+=strlen(rp)+1);
-			if (*rp) {
-				if (ldd_mode) {
-					/* Track which names have been resolved
-					 * and only report each one once. */
-					static unsigned reported;
-					unsigned mask = 1U<<(rp-reserved);
-					if (!(reported & mask)) {
-						reported |= mask;
-						dprintf(1, "\t%s => %s (%p)\n",
-							name, ldso.name,
-							ldso.base);
-					}
+			"c.pthread.rt.m.dl.util.xnet.";
+		const char *rp, *next;
+		for (rp=reserved; *rp; rp=next) {
+			next = strchr(rp, '.') + 1;
+			if (strncmp(name+3, rp, next-rp) == 0)
+				break;
+		}
+		if (*rp) {
+			if (ldd_mode) {
+				/* Track which names have been resolved
+				 * and only report each one once. */
+				static unsigned reported;
+				unsigned mask = 1U<<(rp-reserved);
+				if (!(reported & mask)) {
+					reported |= mask;
+					dprintf(1, "\t%s => %s (%p)\n",
+						name, ldso.name,
+						ldso.base);
 				}
-				is_self = 1;
 			}
+			is_self = 1;
 		}
 	}
 	if (!strcmp(name, ldso.name)) is_self = 1;
-- 
2.10.1

Re: [PATCH] fix ldso reserved library name handling

[Rich Felker]

On Tue, Nov 01, 2016 at 02:49:09AM +0100, Szabolcs Nagy wrote:
> If a DT_NEEDED entry was the prefix of a reserved library name
> (up to the first dot) then it was incorrectly treated as a libc
> reserved name.
> 
> e.g. libp.so dependency was not loaded as it matched libpthread
> reserved name.
> ---
> 
> this is not the smallest possible patch (most of the diff is
> indentation change), but i found the code cleaner without
> the z and l-3 computation.
> 
>  ldso/dynlink.c | 38 +++++++++++++++++++-------------------
>  1 file changed, 19 insertions(+), 19 deletions(-)

The existing code was obviously wrong and this seems to work with
simple testing (dlopen of reserved names still yields self pointer,
dlopen of nonexistent prefixes fails) so I'm committing it. Thanks.

Rich