From: Florian Weimer <firstname.lastname@example.org> To: Rich Felker <email@example.com> Cc: Andreas Schwab <firstname.lastname@example.org>, Al Viro <email@example.com>, "Darrick J. Wong" <firstname.lastname@example.org>, Christoph Hellwig <email@example.com>, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org Subject: Re: XFS reports lchmod failure, but changes file system contents Date: Wed, 12 Feb 2020 21:26:11 +0100 Message-ID: <email@example.com> (raw) In-Reply-To: <20200212201951.GC1663@brightrain.aerifal.cx> (Rich Felker's message of "Wed, 12 Feb 2020 15:19:51 -0500") * Rich Felker: > On Wed, Feb 12, 2020 at 09:17:41PM +0100, Andreas Schwab wrote: >> On Feb 12 2020, Florian Weimer wrote: >> >> > * Al Viro: >> > >> >> On Wed, Feb 12, 2020 at 08:15:08PM +0100, Florian Weimer wrote: >> >> >> >>> | Further, I've found some inconsistent behavior with ext4: chmod on the >> >>> | magic symlink fails with EOPNOTSUPP as in Florian's test, but fchmod >> >>> | on the O_PATH fd succeeds and changes the symlink mode. This is with >> >>> | 5.4. Cany anyone else confirm this? Is it a problem? >> >>> >> >>> It looks broken to me because fchmod (as an inode-changing operation) >> >>> is not supposed to work on O_PATH descriptors. >> >> >> >> Why? O_PATH does have an associated inode just fine; where does >> >> that "not supposed to" come from? >> > >> > It fails on most file systems right now. I thought that was expected. >> > Other system calls (fsetxattr IIRC) do not work on O_PATH descriptors, >> > either. I assumed that an O_PATH descriptor was not intending to >> > confer that capability. Even openat fails. >> >> According to open(2), this is expected: >> >> O_PATH (since Linux 2.6.39) >> Obtain a file descriptor that can be used for two purposes: to >> indicate a location in the filesystem tree and to perform opera- >> tions that act purely at the file descriptor level. The file >> itself is not opened, and other file operations (e.g., read(2), >> write(2), fchmod(2), fchown(2), fgetxattr(2), ioctl(2), mmap(2)) >> fail with the error EBADF. > > That text is outdated and should be corrected. Fixing fchmod fchown, > fstat, etc. to operate on O_PATH file descriptors was a very > intentional change in the kernel. I suppose we could do the S_ISLNK check, try fchmod, and if that fails, go via /proc. Is this the direction you want to go in?
next prev parent reply index Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-02-12 11:48 Florian Weimer 2020-02-12 12:15 ` Florian Weimer 2020-02-12 16:16 ` Darrick J. Wong 2020-02-12 18:11 ` Christoph Hellwig 2020-02-12 18:37 ` Darrick J. Wong 2020-02-12 19:15 ` Florian Weimer 2020-02-12 19:51 ` Al Viro 2020-02-12 19:55 ` Rich Felker 2020-02-12 20:01 ` Florian Weimer 2020-02-12 20:17 ` Andreas Schwab 2020-02-12 20:19 ` Rich Felker 2020-02-12 20:26 ` Florian Weimer [this message] 2020-02-12 20:38 ` Rich Felker 2020-02-12 20:27 ` Al Viro 2020-02-12 20:36 ` Rich Felker 2020-02-12 20:18 ` Rich Felker 2020-02-12 20:38 ` Paul Eggert 2020-02-21 4:09 ` Aleksa Sarai 2020-02-21 5:02 ` Al Viro 2020-02-21 5:21 ` Aleksa Sarai 2020-02-12 18:50 ` Florian Weimer 2020-02-12 18:55 ` Christoph Hellwig
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