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#50012
[PATCH] df: Fixed usage of incorrect stat data when using automount
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Your bug report
#50012: [PATCH] df: Fixed usage of incorrect stat data when using automount
which was filed against the coreutils package, has been closed.
The explanation is attached below, along with your original report.
If you require more details, please reply to 50012 <at> debbugs.gnu.org.
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50012: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=50012
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems
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On 8/11/21 8:59 AM, Thimo Emmerich wrote:
> Since the stat in [2]/df.c, line 1775 is necessary for the following
> fifo evaluation, it seems to be necessary to update the stat information
> after a successful open.
Thanks for reporting the bug. I installed the attached. It differs a bit
from what you proposed in that it prefers fstat to stat, as fstat should
be a bit faster and should avoid some unlikely races (there are many
more races, but one fix at a time).
[0001-df-fix-bug-with-automounted.patch (text/x-patch, attachment)]
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This seems to be a regression from b04ce61958c1: "df: fix hang with fifo
argument".
When using df on an browsable automount map (in my case NFS mounts) df
returns a screwed up information if the mount is not existing.
During execution it triggers the mount via open() but it uses previously
collected stat information for the output.
A second run leads to the correct information due to the mount in the
first run.
Example:
me <at> app07:/psg$ ls -ld psg01bu
drwxr-xr-x 2 root root 0 Jul 23 17:33 psg01bu
me <at> app07:/psg$ df -h psg01bu
Filesystem Size Used Avail Use% Mounted on
auto_psg 2.0T 80M 1.9T 1% /psg
me <at> app07:/psg$ ls -ld psg01bu
drwxrwsr-x 2 root abc 4096 May 5 11:37 psg01bu
me <at> app07:/psg$ df -h psg01bu
Filesystem Size Used Avail Use% Mounted on
fil36:/vg1/lv06/psg01bu 2.0T 80M 1.9T 1% /psg/psg01bu
This behaviour could be observed on Ubuntu 20.04's stock df command
(coreutils 8.30-3ubuntu2) as well as on latest GIT master. An old CentOS
7 machine is not affected.
In general the comment in df.h "stat each of the given entries to make
sure any corresponding partition is automounted." is suspicious since in
[1] it is explicitly stated that "Any access to this directory beyond a
“stat” will (normally) cause the d_op->d_automount() dentry operation to
be called.".
Since the stat in [2]/df.c, line 1775 is necessary for the following
fifo evaluation, it seems to be necessary to update the stat information
after a successful open.
Best regards,
Thimo
[1]: https://www.kernel.org/doc/html/latest/filesystems/autofs.html
[2]: https://github.com/coreutils/coreutils/blob/master/src/df.c#L1775
From a586ab553d9e6f463049349a8ca88d7e727804df Mon Sep 17 00:00:00 2001
From: Thimo Emmerich <thimo.emmerich <at> sony.com>
Date: Wed, 11 Aug 2021 17:50:22 +0200
Subject: [PATCH] df: Fixed usage of incorrect stat data when using automount
This code re-runs stat() after open()ing to update possibly
invalid data. Invalid data can occur in case of using df on
an unmounted directory in a browsable automount map.
---
src/df.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/src/df.c b/src/df.c
index 4534935f5..a5288cb6a 100644
--- a/src/df.c
+++ b/src/df.c
@@ -1766,9 +1766,10 @@ main (int argc, char **argv)
if (optind < argc)
{
- /* stat each of the given entries to make sure any corresponding
- partition is automounted. This must be done before reading the
- file system table. */
+ /* get the stat() information for the fifo check.
+ In case of a browsable automount map this stat will
+ not trigger the mount. Thus the information needs
+ to be updated. */
stats = xnmalloc (argc - optind, sizeof *stats);
for (int i = optind; i < argc; ++i)
{
@@ -1780,10 +1781,15 @@ main (int argc, char **argv)
}
else if (! S_ISFIFO (stats[i - optind].st_mode))
{
- /* open() is needed to automount in some cases. */
+ /* open() each of the given entries to make sure any
corresponding
+ partition is automounted. This must be done before
reading the
+ file system table. */
int fd = open (argv[i], O_RDONLY | O_NOCTTY);
if (0 <= fd)
- close (fd);
+ {
+ close (fd);
+ stat (argv[i], &stats[i - optind]);
+ }
}
}
}
--
2.25.1
--
Mit freundlichen Grüßen / with kind regards
Thimo Emmerich
-------------------------------------------
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Phone: +49 (0) 711 / 5858 - 282
E-mail: thimo.emmerich <at> eu.sony.com
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This bug report was last modified 3 years and 321 days ago.
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