71 lines
2.7 KiB
Diff
71 lines
2.7 KiB
Diff
From: Al Viro <viro@zeniv.linux.org.uk>
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Date: Sun, 26 Jan 2020 09:29:34 -0500
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Subject: do_last(): fetch directory ->i_mode and ->i_uid before it's too late
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Origin: https://git.kernel.org/linus/d0cb50185ae942b03c4327be322055d622dc79f6
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Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2020-8428
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may_create_in_sticky() call is done when we already have dropped the
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reference to dir.
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Fixes: 30aba6656f61e (namei: allow restricted O_CREAT of FIFOs and regular files)
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Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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[Salvatore Bonaccorso: Backport to 4.19.98 for context changes]
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---
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fs/namei.c | 17 ++++++++++-------
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1 file changed, 10 insertions(+), 7 deletions(-)
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--- a/fs/namei.c
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+++ b/fs/namei.c
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@@ -1009,7 +1009,8 @@ static int may_linkat(struct path *link)
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* may_create_in_sticky - Check whether an O_CREAT open in a sticky directory
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* should be allowed, or not, on files that already
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* exist.
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- * @dir: the sticky parent directory
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+ * @dir_mode: mode bits of directory
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+ * @dir_uid: owner of directory
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* @inode: the inode of the file to open
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*
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* Block an O_CREAT open of a FIFO (or a regular file) when:
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@@ -1025,18 +1026,18 @@ static int may_linkat(struct path *link)
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*
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* Returns 0 if the open is allowed, -ve on error.
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*/
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-static int may_create_in_sticky(struct dentry * const dir,
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+static int may_create_in_sticky(umode_t dir_mode, kuid_t dir_uid,
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struct inode * const inode)
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{
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if ((!sysctl_protected_fifos && S_ISFIFO(inode->i_mode)) ||
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(!sysctl_protected_regular && S_ISREG(inode->i_mode)) ||
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- likely(!(dir->d_inode->i_mode & S_ISVTX)) ||
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- uid_eq(inode->i_uid, dir->d_inode->i_uid) ||
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+ likely(!(dir_mode & S_ISVTX)) ||
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+ uid_eq(inode->i_uid, dir_uid) ||
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uid_eq(current_fsuid(), inode->i_uid))
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return 0;
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- if (likely(dir->d_inode->i_mode & 0002) ||
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- (dir->d_inode->i_mode & 0020 &&
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+ if (likely(dir_mode & 0002) ||
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+ (dir_mode & 0020 &&
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((sysctl_protected_fifos >= 2 && S_ISFIFO(inode->i_mode)) ||
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(sysctl_protected_regular >= 2 && S_ISREG(inode->i_mode))))) {
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return -EACCES;
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@@ -3258,6 +3259,8 @@ static int do_last(struct nameidata *nd,
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struct file *file, const struct open_flags *op)
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{
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struct dentry *dir = nd->path.dentry;
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+ kuid_t dir_uid = dir->d_inode->i_uid;
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+ umode_t dir_mode = dir->d_inode->i_mode;
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int open_flag = op->open_flag;
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bool will_truncate = (open_flag & O_TRUNC) != 0;
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bool got_write = false;
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@@ -3393,7 +3396,7 @@ finish_open:
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error = -EISDIR;
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if (d_is_dir(nd->path.dentry))
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goto out;
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- error = may_create_in_sticky(dir,
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+ error = may_create_in_sticky(dir_mode, dir_uid,
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d_backing_inode(nd->path.dentry));
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if (unlikely(error))
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goto out;
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