[PATCH v3 04/18] eal: fix plugin dir walk

[David Marchand <david.marchand@redhat.com>]

For '.' and '..' directories (or any short file name),
a out of bound issue occurs.

Caught by UBSan:

EAL: Detected shared linkage of DPDK
../lib/eal/common/eal_common_options.c:420:15: runtime error: index -2
	out of bounds for type 'char[256]'
    #0 0x7f867eedf206 in eal_plugindir_init
	eal_common_options.c
    #1 0x7f867eede58a in eal_plugins_init
	(build/lib/librte_eal.so.25+0xde58a)
	(BuildId: e7e4a1935e4bacb51c82ab1a84098a27decf3b4c)
    #2 0x7f867efb8587 in rte_eal_init
	(build/lib/librte_eal.so.25+0x1b8587)
	(BuildId: e7e4a1935e4bacb51c82ab1a84098a27decf3b4c)
    #3 0x55b62360861e in main
	(/home/runner/work/dpdk/dpdk/build/app/dpdk-testpmd+0x9e061e)
	(BuildId: d821ec918612c83fad8b5ccb6cc518e66bee48cd)
    #4 0x7f8667429d8f in __libc_start_call_main
	csu/../sysdeps/nptl/libc_start_call_main.h:58:16
    #5 0x7f8667429e3f in __libc_start_main
	csu/../csu/libc-start.c:392:3
    #6 0x55b622d9d444 in _start
	(/home/runner/work/dpdk/dpdk/build/app/dpdk-testpmd+0x175444)
	(BuildId: d821ec918612c83fad8b5ccb6cc518e66bee48cd)
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior
	../lib/eal/common/eal_common_options.c:420:15 in
	../lib/eal/common/eal_common_options.c:421:15:
	runtime error: index 18446744073709551609 out of bounds
	for type 'char[256]'

Fixes: c57f6e5c604a ("eal: fix plugin loading")
Cc: stable@dpdk.org

Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
---
Changes since v2:
- removed check on null termination of dirent,

---
 lib/eal/common/eal_common_options.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/lib/eal/common/eal_common_options.c b/lib/eal/common/eal_common_options.c
index f0a9ddeeb7..e6eb04a138 100644
--- a/lib/eal/common/eal_common_options.c
+++ b/lib/eal/common/eal_common_options.c
@@ -399,12 +399,21 @@ eal_plugins_init(void)
 }
 #else
 
+static bool
+ends_with(const char *str, const char *tail)
+{
+	size_t tail_len = strlen(tail);
+	size_t str_len = strlen(str);
+
+	return str_len >= tail_len && strcmp(&str[str_len - tail_len], tail) == 0;
+}
+
 static int
 eal_plugindir_init(const char *path)
 {
-	DIR *d = NULL;
 	struct dirent *dent = NULL;
 	char sopath[PATH_MAX];
+	DIR *d = NULL;
 
 	if (path == NULL || *path == '\0')
 		return 0;
@@ -418,12 +427,8 @@ eal_plugindir_init(const char *path)
 
 	while ((dent = readdir(d)) != NULL) {
 		struct stat sb;
-		int nlen = strnlen(dent->d_name, sizeof(dent->d_name));
 
-		/* check if name ends in .so or .so.ABI_VERSION */
-		if (strcmp(&dent->d_name[nlen - 3], ".so") != 0 &&
-		    strcmp(&dent->d_name[nlen - 4 - strlen(ABI_VERSION)],
-			   ".so."ABI_VERSION) != 0)
+		if (!ends_with(dent->d_name, ".so") && !ends_with(dent->d_name, ".so."ABI_VERSION))
 			continue;
 
 		snprintf(sopath, sizeof(sopath), "%s/%s", path, dent->d_name);
-- 
2.50.0