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Subject: |
[PATCH] df: Fixed usage of incorrect stat data when using automount |
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Date: |
Wed, 11 Aug 2021 17:59:29 +0200 |
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Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.11.0 |
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@app07:/psg$ ls -ld psg01bu
drwxr-xr-x 2 root root 0 Jul 23 17:33 psg01bu
me@app07:/psg$ df -h psg01bu
Filesystem Size Used Avail Use% Mounted on
auto_psg 2.0T 80M 1.9T 1% /psg
me@app07:/psg$ ls -ld psg01bu
drwxrwsr-x 2 root abc 4096 May 5 11:37 psg01bu
me@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@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
-------------------------------------------
R&D Center Europe Stuttgart Laboratory 01
Phone: +49 (0) 711 / 5858 - 282
E-mail: thimo.emmerich@eu.sony.com
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Incorporated in the Netherlands No. 71682147
Directors: Hideyuki Furumi, Masaki Kurebayashi, Ricky Londema
--- End Message ---
--- Begin Message ---
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Subject: |
Re: bug#50012: [PATCH] df: Fixed usage of incorrect stat data when using automount |
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Date: |
Wed, 11 Aug 2021 11:24:03 -0700 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 |
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
Description: Text Data
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