Bug 222698 - [patch] find(1)'s -newer expression doesn't work with symbolic links if '-P' (the default) is requested.
Summary: [patch] find(1)'s -newer expression doesn't work with symbolic links if '-P' ...
Status: Closed FIXED
Alias: None
Product: Base System
Classification: Unclassified
Component: bin (show other bugs)
Version: CURRENT
Hardware: Any Any
: --- Affects Many People
Assignee: Conrad Meyer
Keywords: patch
Depends on:
Reported: 2017-09-30 12:37 UTC by Harald Schmalzbauer
Modified: 2017-12-31 20:35 UTC (History)
2 users (show)

See Also:


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Description Harald Schmalzbauer 2017-09-30 12:37:18 UTC
Utilizing find(1)'s 'newer' primary expression is broken with symbolic links.

According to the man page, -P should be the default behaviour, but even if explicitly defining -P, find uses timestamp information from the file referenced by the link, not the link itself.

To see in action (copy'n'pastable for sh and csh):

[ -e /tmp/find-test ] && rm -R /tmp/find-test
mkdir /tmp/find-test && cd /tmp/find-test
ln -s fILE lINK-to-fILE && sleep 1
echo "Created after lINK-to-fILE" > fILE2 && sleep 1
echo "Newest in the hood" > fILE && sleep 1
find . -newermm lINK-to-fILE

It doesn't return fILE2 nor fILE, while stat(1) clearly confirms newer m_times for fILE and fILE2 compared to lINK-to-fILE ( 'stat -f "%N: %Sm" *' ).

It's possible that find(1) hasn't been working like expected for a quiet long time.  I first recognized strange results arround FreeBSD 8.0 but haven't had time|need to investigate.
More precisely, I thought that the error was in my backup script due to timestamp precision changes, which changed around that time if I remember correctly.  But since timestamp comparings is a fallback mechanism in my script, never needed until yesterday in real world, I haven't paid any attention until today.

To falsify find(1)'s misbehaviour, continue the test above with:

touch -m -t `stat -f %Sm -t %y%m%d%H%M.%S lINK-to-fILE` fILE
find . -newermm lINK-to-fILE

Now you get the result which was expected before.

Why don't I just use 'touch -r' ?  Well, tried that of course, but I had to find out that touch(1) is not using the m_time of the link, but from the file referenced by the link.  touch(1) hasn't options which influence that and doesn't state default behaviour...

Will see if I can identify the problem in the source of find(1) and add comments as soon as I found anything.
But I hope people with better C skills jump in!

Even if it's a old bug, it's a very nasty one, because it can affect user's data...  So high priority IMHO.

Comment 1 Conrad Meyer freebsd_committer 2017-12-28 19:36:42 UTC
Here the behavior is described in the POSIX 2008, 2016 edition standard: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/find.html

Harald is correct that the default behavior (and for -H, traversed paths) should use the metadata for the link itself, rather than that of the referenced file.
Comment 2 Conrad Meyer freebsd_committer 2017-12-28 19:42:49 UTC
fstatfs(5,{ fstypename=ufs,mntonname=/,mntfromname=/dev/gpt/freebsd-root,fsid= }) = 0 (0x0)
fstat(5,{ mode=drwxr-xr-x ,inode=42455429,size=512,blksize=32768 }) = 0 (0x0)
fchdir(0x5)                                      = 0 (0x0)
getdirentries(5,"\M^E\M-Q\M^G\^B\0\0\0\0\0\0\0\0"...,4096,{ 0x0 }) = 168 (0xa8)
fstatat(AT_FDCWD,"lINK-to-fILE",{ mode=lrwxr-xr-x ,inode=42459218,size=4,blksize=32768 },AT_SYMLINK_NOFOLLOW) = 0 (0x0)
fstatat(AT_FDCWD,"fILE2",{ mode=-rw-r--r-- ,inode=42459473,size=27,blksize=32768 },AT_SYMLINK_NOFOLLOW) = 0 (0x0)
fstatat(AT_FDCWD,"fILE",{ mode=-rw-r--r-- ,inode=42459474,size=19,blksize=32768 },AT_SYMLINK_NOFOLLOW) = 0 (0x0)
getdirentries(5,0x8006a8000,4096,{ 0x200 })      = 0 (0x0)
close(5)                                         = 0 (0x0)

So we see that find(1) is correctly using AT_SYMLINK_NOFOLLOW to obtain stat information for the symlink, as well as the other files.  So either the kernel is broken, or the comparison is somehow broken.
Comment 3 Conrad Meyer freebsd_committer 2017-12-28 19:49:37 UTC
(In reply to Conrad Meyer from comment #2)
Ah, that is during traversal.  For the reference file (the "plan"), find(1) is incorrectly using fstatat without the NOFOLLOW flag:

fstatat(AT_FDCWD,"lINK-to-fILE",{ mode=-rw-r--r-- ,inode=42459474,size=19,blksize=32768 },0x0) = 0 (0x0)
Comment 4 Conrad Meyer freebsd_committer 2017-12-28 19:57:47 UTC
This change ought to be sufficient to fix -newer:

--- a/usr.bin/find/function.c
+++ b/usr.bin/find/function.c
@@ -1201,6 +1201,7 @@ c_newer(OPTION *option, char ***argvp)
        char *fn_or_tspec;
        PLAN *new;
        struct stat sb;
+       int error;

        fn_or_tspec = nextarg(option, argvp);
        ftsoptions &= ~FTS_NOSTAT;
@@ -1214,7 +1215,11 @@ c_newer(OPTION *option, char ***argvp)
                /* Use the seconds only in the comparison. */
                new->t_data.tv_nsec = 999999999;
        } else {
-               if (stat(fn_or_tspec, &sb))
+               if (ftsoptions & FTS_PHYSICAL)
+                       error = lstat(fn_or_tspec, &sb);
+               else
+                       error = stat(fn_or_tspec, &sb);
+               if (error != 0)
                        err(1, "%s", fn_or_tspec);
                if (option->flags & F_TIME2_C)
                        new->t_data = sb.st_ctim;

However, -samefile is similarly broken.  Here's a patch for that part:

--- a/usr.bin/find/function.c
+++ b/usr.bin/find/function.c
@@ -1066,12 +1066,17 @@ c_samefile(OPTION *option, char ***argvp)
        char *fn;
        PLAN *new;
        struct stat sb;
+       int error;

        fn = nextarg(option, argvp);
        ftsoptions &= ~FTS_NOSTAT;

        new = palloc(option);
-       if (stat(fn, &sb))
+       if (ftsoptions & FTS_PHYSICAL)
+               error = lstat(fn, &sb);
+       else
+               error = stat(fn, &sb);
+       if (error != 0)
                err(1, "%s", fn);
        new->i_data = sb.st_ino;
        return new;
Comment 5 Conrad Meyer freebsd_committer 2017-12-28 19:59:02 UTC
This has apparently been broken since inclusion in 2001 (r76250) of a patch originally submitted in 1999.
Comment 6 Conrad Meyer freebsd_committer 2017-12-28 20:00:15 UTC
No, hold on, it was broken even before that, in the BSD 4.4-Lite source import: r1590.  Probably broken from the dawn of CSRG.
Comment 7 Harald Schmalzbauer 2017-12-29 07:34:31 UTC
Thanks a lot Conrad!
I spent an hour on this back than and reached the same point in code (as far as I remember), but wasn't even close to your solution.  My result was more like pigs staring at clockworks ... :-(

But I checked different sources and also all linux versions I found had the same erroneous implementation.
Glad you finally made it POSIX/man page compatible (after 20+ years?!?).

Unfortunately I don't have time to do any tests, but I don't think there's a need for testing if the example show correct behaviour now.

Have an guadn Rutsch!

Comment 8 Conrad Meyer freebsd_committer 2017-12-29 22:09:01 UTC
Happy new years!
Comment 9 commit-hook freebsd_committer 2017-12-29 22:09:20 UTC
A commit references this bug:

Author: cem
Date: Fri Dec 29 22:08:44 UTC 2017
New revision: 327362
URL: https://svnweb.freebsd.org/changeset/base/327362

  find(1): Fix -newer and -samefile to conform to POSIX[0]

  By default, or with the -P flag, find(1) should evaluate paths "physically."
  For symlinks, this means using the link itself instead of the target.

  Historically (since the import of BSD 4.4-lite from CSRG), find(1) has
  failed to refer to the link itself, at least for -newer and -samefile.

  [0]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/find.html

  PR:		222698
  Reported by:	Harald Schmalzbauer <bugzilla.freebsd AT omnilan.de>
  Sponsored by:	Dell EMC Isilon

Comment 10 Jilles Tjoelker freebsd_committer 2017-12-31 20:35:07 UTC
What should happen in -H mode (half-logical; symlinks mentioned on the command line are followed but symlinks found in a directory tree walk are not)?

A literal interpretation of POSIX (with the assumption that auxiliary arguments work the same way as primary arguments) would be that symlinks should be followed, but in the case of -samefile this makes it non-reflexive.