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ln: Refuse deleting a directory entry by hardlinking it to itself.

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Two pathnames refer to the same directory entry iff the directories match
and the final components' names match.

Example: (assuming file1 is an existing file)
  ln -f file1 file1
This now fails while leaving file1 intact. It used to delete file1 and then
complain it cannot be linked because it is gone.

With -i, this error is detected before the question is asked.

MFC after:	2 weeks
This commit is contained in:
Jilles Tjoelker 2010-04-17 22:39:53 +00:00
parent 9eb448a7e6
commit 5d66b54e27
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=206773
1 changed files with 59 additions and 2 deletions
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61
bin/ln/ln.c
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@ -172,6 +172,52 @@ main(int argc, char *argv[])
exit(exitval);
}
/*
* Two pathnames refer to the same directory entry if the directories match
* and the final components' names match.
*/
static int
samedirent(const char *path1, const char *path2)
{
const char *file1, *file2;
char pathbuf[PATH_MAX];
struct stat sb1, sb2;
if (strcmp(path1, path2) == 0)
return 1;
file1 = strrchr(path1, '/');
if (file1 != NULL)
file1++;
else
file1 = path1;
file2 = strrchr(path2, '/');
if (file2 != NULL)
file2++;
else
file2 = path2;
if (strcmp(file1, file2) != 0)
return 0;
if (file1 - path1 >= PATH_MAX || file2 - path2 >= PATH_MAX)
return 0;
if (file1 == path1)
memcpy(pathbuf, ".", 2);
else {
memcpy(pathbuf, path1, file1 - path1);
pathbuf[file1 - path1] = '\0';
}
if (stat(pathbuf, &sb1) != 0)
return 0;
if (file2 == path2)
memcpy(pathbuf, ".", 2);
else {
memcpy(pathbuf, path2, file2 - path2);
pathbuf[file2 - path2] = '\0';
}
if (stat(pathbuf, &sb2) != 0)
return 0;
return sb1.st_dev == sb2.st_dev && sb1.st_ino == sb2.st_ino;
}
int
linkit(const char *source, const char *target, int isdir)
{
@ -215,7 +261,6 @@ linkit(const char *source, const char *target, int isdir)
target = path;
}
exists = !lstat(target, &sb);
/*
* If the link source doesn't exist, and a symbolic link was
* requested, and -w was specified, give a warning.
@ -242,8 +287,20 @@ linkit(const char *source, const char *target, int isdir)
warn("warning: %s", source);
}
}
/*
* If the file exists, then unlink it forcibly if -f was specified
* If the file exists, first check it is not the same directory entry.
*/
exists = !lstat(target, &sb);
if (exists) {
if (!sflag && samedirent(source, target)) {
warnx("%s and %s are the same directory entry",
source, target);
return (1);
}
}
/*
* Then unlink it forcibly if -f was specified
* and interactively if -i was specified.
*/
if (fflag && exists) {