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From:   Max Staudt <max@enpas.org>
To:     David Sterba <dsterba@suse.com>
Cc:     linux-fsdevel@vger.kernel.org,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        linux-m68k@lists.linux-m68k.org, glaubitz@physik.fu-berlin.de,
        linux-kernel@vger.kernel.org, Max Staudt <max@enpas.org>,
        stable@vger.kernel.org
Subject: [PATCH] fs/affs: Fix basic permission bits to actually work
Date:   Thu, 27 Aug 2020 17:49:00 +0200
Message-Id: <20200827154900.28233-1-max@enpas.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
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The basic permission bits (protection bits in AmigaOS) have been broken
in Linux' affs - it would only set bits, but never delete them.
Also, contrary to the documentation, the Archived bit was not handled.

Let's fix this for good, and set the bits such that Linux and classic
AmigaOS can coexist in the most peaceful manner.

Also, update the documentation to represent the current state of things.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Max Staudt <max@enpas.org>
---
 Documentation/filesystems/affs.rst | 16 ++++++++++------
 fs/affs/amigaffs.c                 | 27 +++++++++++++++++++++++++++
 fs/affs/file.c                     | 27 ++++++++++++++++++++++++++-
 3 files changed, 63 insertions(+), 7 deletions(-)

diff --git a/Documentation/filesystems/affs.rst b/Documentation/filesystems/affs.rst
index 7f1a40dce6d3..5776cbd5fa53 100644
--- a/Documentation/filesystems/affs.rst
+++ b/Documentation/filesystems/affs.rst
@@ -110,13 +110,15 @@ The Amiga protection flags RWEDRWEDHSPARWED are handled as follows:
 
   - R maps to r for user, group and others. On directories, R implies x.
 
-  - If both W and D are allowed, w will be set.
+  - W maps to w.
 
   - E maps to x.
 
-  - H and P are always retained and ignored under Linux.
+  - D is ignored.
 
-  - A is always reset when a file is written to.
+  - H, S and P are always retained and ignored under Linux.
+
+  - A is cleared when a file is written to.
 
 User id and group id will be used unless set[gu]id are given as mount
 options. Since most of the Amiga file systems are single user systems
@@ -128,11 +130,13 @@ Linux -> Amiga:
 
 The Linux rwxrwxrwx file mode is handled as follows:
 
-  - r permission will set R for user, group and others.
+  - r permission will allow R for user, group and others.
+
+  - w permission will allow W for user, group and others.
 
-  - w permission will set W and D for user, group and others.
+  - x permission of the user will allow E for plain files.
 
-  - x permission of the user will set E for plain files.
+  - D will be allowed for user, group and others.
 
   - All other flags (suid, sgid, ...) are ignored and will
     not be retained.
diff --git a/fs/affs/amigaffs.c b/fs/affs/amigaffs.c
index f708c45d5f66..7952f885e6c6 100644
--- a/fs/affs/amigaffs.c
+++ b/fs/affs/amigaffs.c
@@ -420,24 +420,51 @@ affs_mode_to_prot(struct inode *inode)
 	u32 prot = AFFS_I(inode)->i_protect;
 	umode_t mode = inode->i_mode;
 
+	/*
+	 * First, clear all RWED bits for owner, group, other.
+	 * Then, recalculate them afresh.
+	 *
+	 * We'll always clear the delete-inhibit bit for the owner,
+	 * as that is the classic single-user mode AmigaOS protection
+	 * bit and we need to stay compatible with all scenarios.
+	 *
+	 * Since multi-user AmigaOS is an extension, we'll only set
+	 * the delete-allow bit if any of the other bits in the same
+	 * user class (group/other) are used.
+	 */
+	prot &= ~(FIBF_NOEXECUTE | FIBF_NOREAD
+		  | FIBF_NOWRITE | FIBF_NODELETE
+		  | FIBF_GRP_EXECUTE | FIBF_GRP_READ
+		  | FIBF_GRP_WRITE   | FIBF_GRP_DELETE
+		  | FIBF_OTR_EXECUTE | FIBF_OTR_READ
+		  | FIBF_OTR_WRITE   | FIBF_OTR_DELETE);
+
+	/* Classic single-user AmigaOS flags. These are inverted. */
 	if (!(mode & 0100))
 		prot |= FIBF_NOEXECUTE;
 	if (!(mode & 0400))
 		prot |= FIBF_NOREAD;
 	if (!(mode & 0200))
 		prot |= FIBF_NOWRITE;
+
+	/* Multi-user extended flags. Not inverted. */
 	if (mode & 0010)
 		prot |= FIBF_GRP_EXECUTE;
 	if (mode & 0040)
 		prot |= FIBF_GRP_READ;
 	if (mode & 0020)
 		prot |= FIBF_GRP_WRITE;
+	if (mode & 0070)
+		prot |= FIBF_GRP_DELETE;
+
 	if (mode & 0001)
 		prot |= FIBF_OTR_EXECUTE;
 	if (mode & 0004)
 		prot |= FIBF_OTR_READ;
 	if (mode & 0002)
 		prot |= FIBF_OTR_WRITE;
+	if (mode & 0007)
+		prot |= FIBF_OTR_DELETE;
 
 	AFFS_I(inode)->i_protect = prot;
 }
diff --git a/fs/affs/file.c b/fs/affs/file.c
index a26a0f96c119..9a137e2f1782 100644
--- a/fs/affs/file.c
+++ b/fs/affs/file.c
@@ -429,6 +429,25 @@ static int affs_write_begin(struct file *file, struct address_space *mapping,
 	return ret;
 }
 
+static int affs_write_end(struct file *file, struct address_space *mapping,
+			  loff_t pos, unsigned int len, unsigned int copied,
+			  struct page *page, void *fsdata)
+{
+	struct inode *inode = mapping->host;
+	int ret;
+
+	ret = generic_write_end(file, mapping, pos, len, copied,
+				page, fsdata);
+
+	/* Clear Archived bit on file writes, as AmigaOS would do */
+	if (AFFS_I(inode)->i_protect & FIBF_ARCHIVED) {
+		AFFS_I(inode)->i_protect &= ~FIBF_ARCHIVED;
+		mark_inode_dirty(inode);
+	}
+
+	return ret;
+}
+
 static sector_t _affs_bmap(struct address_space *mapping, sector_t block)
 {
 	return generic_block_bmap(mapping,block,affs_get_block);
@@ -438,7 +457,7 @@ const struct address_space_operations affs_aops = {
 	.readpage = affs_readpage,
 	.writepage = affs_writepage,
 	.write_begin = affs_write_begin,
-	.write_end = generic_write_end,
+	.write_end = affs_write_end,
 	.direct_IO = affs_direct_IO,
 	.bmap = _affs_bmap
 };
@@ -795,6 +814,12 @@ static int affs_write_end_ofs(struct file *file, struct address_space *mapping,
 	if (tmp > inode->i_size)
 		inode->i_size = AFFS_I(inode)->mmu_private = tmp;
 
+	/* Clear Archived bit on file writes, as AmigaOS would do */
+	if (AFFS_I(inode)->i_protect & FIBF_ARCHIVED) {
+		AFFS_I(inode)->i_protect &= ~FIBF_ARCHIVED;
+		mark_inode_dirty(inode);
+	}
+
 err_first_bh:
 	unlock_page(page);
 	put_page(page);
-- 
2.20.1