Commit 42cb56ae authored Sep 18, 2009 by Jeff Layton Committed by Al Viro Sep 24, 2009

vfs: change sb->s_maxbytes to a loff_t



sb->s_maxbytes is supposed to indicate the maximum size of a file that can
exist on the filesystem.  It's declared as an unsigned long long.

Even if a filesystem has no inherent limit that prevents it from using
every bit in that unsigned long long, it's still problematic to set it to
anything larger than MAX_LFS_FILESIZE.  There are places in the kernel
that cast s_maxbytes to a signed value.  If it's set too large then this
cast makes it a negative number and generally breaks the comparison.

Change s_maxbytes to be loff_t instead.  That should help eliminate the
temptation to set it too large by making it a signed value.

Also, add a warning for couple of releases to help catch filesystems that
set s_maxbytes too large.  Eventually we can either convert this to a
BUG() or just remove it and in the hope that no one will get it wrong now
that it's a signed value.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Robert Love <rlove@google.com>
Cc: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

parent 5aa98b70

fs/super.c

+10 −0

Original line number	Diff line number	Diff line
		@@ -892,6 +892,16 @@ vfs_kern_mount(struct file_system_type type, int flags, const char name, void
		if (error)
		goto out_sb;

		/*
		* filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
		* but s_maxbytes was an unsigned long long for many releases. Throw
		* this warning for a little while to try and catch filesystems that
		* violate this rule. This warning should be either removed or
		* converted to a BUG() in 2.6.34.
		*/
		WARN((mnt->mnt_sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
		"negative value (%lld)\n", type->name, mnt->mnt_sb->s_maxbytes);

		mnt->mnt_mountpoint = mnt->mnt_root;
		mnt->mnt_parent = mnt;
		up_write(&mnt->mnt_sb->s_umount);

include/linux/fs.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -1315,7 +1315,7 @@ struct super_block {
		unsigned long s_blocksize;
		unsigned char s_blocksize_bits;
		unsigned char s_dirt;
		unsigned long long s_maxbytes; /* Max file size */
		loff_t s_maxbytes; /* Max file size */
		struct file_system_type *s_type;
		const struct super_operations *s_op;
		const struct dquot_operations *dq_op;

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