Re: [PATCH 00/25] move handling of setuid/gid bits from VFS into individual setattr functions (RESEND)
From: Jeff Layton <hidden>
Date: 2007-08-13 12:36:16
Also in:
linux-ext4, linux-fsdevel, lkml
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
On Mon, 13 Aug 2007 08:01:34 -0400 Jeff Layton [off-list ref] wrote:
On Sat, 11 Aug 2007 03:57:39 +0100 Christoph Hellwig [off-list ref] wrote:quoted
I like the idea of checking ia_valid after return a lot. But instead of going BUG() it should just do the default action, that we can avoid touching all the filesystem and only need to change those that need special care. I also have plans to add some new AT_ flags for implementing some filesystem ioctl in generic code that would benefit greatly from the ia_valid checkin after return to return ENOTTY fr filesystems not implementing those ioctls.That sounds good (if I follow your meaning correctly). How about something like the patch below? If either ATTR_KILL bit is set after the setattr, try to handle them in the "standard" way with a second setattr call. It also does a printk in this situation to alert filesystem developers that they should convert to the "new" scheme, so they can avoid this second setattr call. If this idea seems sound then I'll start the grunt work to fix up the in-tree filesystems so that they don't need the second setattr call.
The earlier patch has a misplaced comma and won't build. This one
builds. This should be considered an RFC, as I've not yet done any
real testing of this patch:
Signed-off-by: Jeff Layton <redacted>
commit ad00450c4532da32718efe39e27d99060f04e396
Author: Jeff Layton [off-list ref]
Date: Mon Aug 13 08:33:10 2007 -0400
VFS: move ATTR_KILL handling from notify_change into helper function
Separate the handling of the local ia_valid bitmask from the one in
attr->ia_valid. This allows us to hand off the actual handling of the
ATTR_KILL_* flags to the .setattr i_op when one is defined.
notify_change still needs to process those flags for the local ia_valid
variable, since it uses that to decide whether to return early, and to pass
a (hopefully) appropriate bitmask to fsnotify_change.
Also, check the ia_valid after the setattr op returns and see if either
ATTR_KILL_* bit is set. If so, then throw a warning and try to clear the
bits in the "standard" way. This should help us to catch filesystems that
don't handle these bits correctly without breaking them outright.
diff --git a/fs/attr.c b/fs/attr.c
index f8dfc22..9585e45 100644
--- a/fs/attr.c
+++ b/fs/attr.c@@ -100,15 +100,53 @@ int inode_setattr(struct inode * inode, struct iattr * attr) } EXPORT_SYMBOL(inode_setattr); +/** + * generic_attrkill - helper to convert ATTR_KILL_* bits into mode change + * @mode: current mode of inode + * @attr: inode attribute changes requested by VFS + * Context: anywhere + * + * This is a helper function to convert ATTR_KILL_SUID and ATTR_KILL_SGID + * into a mode change. Filesystems should call this from their setattr + * inode op when they want "conventional" setuid-clearing behavior. + * + * Filesystems that declare a setattr inode operation are now expected to + * handle the ATTR_KILL_SUID and ATTR_KILL_SGID bits appropriately. The VFS + * no longer automatically converts these bits to a mode change for + * inodes that have their own setattr operation. + **/ +void generic_attrkill(mode_t mode, struct iattr *attr) +{ + if (attr->ia_valid & ATTR_KILL_SUID) { + attr->ia_valid &= ~ATTR_KILL_SUID; + if (mode & S_ISUID) { + if (!(attr->ia_valid & ATTR_MODE)) { + attr->ia_valid |= ATTR_MODE; + attr->ia_mode = mode; + } + attr->ia_mode &= ~S_ISUID; + } + } + if (attr->ia_valid & ATTR_KILL_SGID) { + attr->ia_valid &= ~ATTR_KILL_SGID; + if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) { + if (!(attr->ia_valid & ATTR_MODE)) { + attr->ia_valid |= ATTR_MODE; + attr->ia_mode = mode; + } + attr->ia_mode &= ~S_ISGID; + } + } +} +EXPORT_SYMBOL(generic_attrkill); + int notify_change(struct dentry * dentry, struct iattr * attr) { struct inode *inode = dentry->d_inode; - mode_t mode; - int error; + int error, once = 0; struct timespec now; unsigned int ia_valid = attr->ia_valid; - mode = inode->i_mode; now = current_fs_time(inode->i_sb); attr->ia_ctime = now;
@@ -117,36 +155,48 @@ int notify_change(struct dentry * dentry, struct iattr * attr) if (!(ia_valid & ATTR_MTIME_SET)) attr->ia_mtime = now; if (ia_valid & ATTR_KILL_SUID) { - attr->ia_valid &= ~ATTR_KILL_SUID; - if (mode & S_ISUID) { - if (!(ia_valid & ATTR_MODE)) { - ia_valid = attr->ia_valid |= ATTR_MODE; - attr->ia_mode = inode->i_mode; - } - attr->ia_mode &= ~S_ISUID; - } + ia_valid &= ~ATTR_KILL_SUID; + if (inode->i_mode & S_ISUID) + ia_valid |= ATTR_MODE; } if (ia_valid & ATTR_KILL_SGID) { - attr->ia_valid &= ~ ATTR_KILL_SGID; - if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) { - if (!(ia_valid & ATTR_MODE)) { - ia_valid = attr->ia_valid |= ATTR_MODE; - attr->ia_mode = inode->i_mode; - } - attr->ia_mode &= ~S_ISGID; - } + ia_valid &= ~ATTR_KILL_SGID; + if ((inode->i_mode & (S_ISGID | S_IXGRP)) == + (S_ISGID | S_IXGRP)) + ia_valid |= ATTR_MODE; } - if (!attr->ia_valid) + if (!ia_valid) return 0; if (ia_valid & ATTR_SIZE) down_write(&dentry->d_inode->i_alloc_sem); if (inode->i_op && inode->i_op->setattr) { +try_again: error = security_inode_setattr(dentry, attr); if (!error) error = inode->i_op->setattr(dentry, attr); + /* + * if ATTR_KILL_SUID or ATTR_KILL_SGID is still set, then + * assume that the setattr inode op didn't handle them + * correctly. Try to clear these bits the standard way + * and throw a warning. + */ + if (!error && !once && unlikely(attr->ia_valid & + (ATTR_KILL_SUID|ATTR_KILL_SGID))) { + attr->ia_valid &= + (ATTR_MODE|ATTR_KILL_SUID|ATTR_KILL_SGID); + generic_attrkill(inode->i_mode, attr); + once = 1; + if (printk_ratelimit()) + printk(KERN_ERR "%s: %s doesn't seem to " + "handle setuid/setgid bit clearing " + "correctly.\n", __func__, + inode->i_sb->s_type->name); + goto try_again; + } } else { + generic_attrkill(inode->i_mode, attr); error = inode_change_ok(inode, attr); if (!error) error = security_inode_setattr(dentry, attr);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6bf1395..daac0e5 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h@@ -1561,6 +1561,7 @@ extern int do_remount_sb(struct super_block *sb, int flags, #ifdef CONFIG_BLOCK extern sector_t bmap(struct inode *, sector_t); #endif +extern void generic_attrkill(mode_t mode, struct iattr *attr); extern int notify_change(struct dentry *, struct iattr *); extern int permission(struct inode *, int, struct nameidata *); extern int generic_permission(struct inode *, int,