lsof: correct check for symbolic link

Busybox lsof used the d_type field of a 'struct dirent' to verify whether the
entry is a symbolic link. This field, however, is not portable. On at least
one board [1] I have seen, that field is 0, and the check fails even though
the entry is a link.

The explicit check for a symbolic link is really only needed to skip the
default directory entries '.' and '..'. The directory /proc/<pid>/fd/
should not contain anything else but these two and symbolic links.
With these assumptions, this patch replaces the explicit link check with a
basic check for '.' and '..' (and any hidden file). In the unlikely case that
there are other file types, xmalloc_readlink() will return NULL, and we can
skip the entry.

[1] A MIPS-based board with glibc 2.9, Linux 2.6.32.27.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/procps/lsof.c b/procps/lsof.c
index 7e0ffa4e5..b0156a538 100644
--- a/procps/lsof.c
+++ b/procps/lsof.c
@@ -61,9 +61,12 @@ int lsof_main(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
                 d_fd = opendir(name);
                 if (d_fd) {
                         while ((entry = readdir(d_fd)) != NULL) {
-                                if (entry->d_type == DT_LNK) {
-                                        safe_strncpy(name + baseofs, entry->d_name, 10);
-                                        fdlink = xmalloc_readlink(name);
+                                /* Skip entries '.' and '..' (and any hidden file) */
+                                if (entry->d_name[0] == '.')
+                                        continue;
+
+                                safe_strncpy(name + baseofs, entry->d_name, 10);
+                                if ((fdlink = xmalloc_readlink(name)) != NULL) {
                                         printf("%d\t%s\t%s\n", proc->pid, proc->exe, fdlink);
                                         free(fdlink);
                                 }