vt: keyboard, extend func_buf_lock to readers
commit5.4-rM2-2.2.x-imx-squashed82e61c3909
upstream. Both read-side users of func_table/func_buf need locking. Without that, one can easily confuse the code by repeatedly setting altering strings like: while (1) for (a = 0; a < 2; a++) { struct kbsentry kbs = {}; strcpy((char *)kbs.kb_string, a ? ".\n" : "88888\n"); ioctl(fd, KDSKBSENT, &kbs); } When that program runs, one can get unexpected output by holding F1 (note the unxpected period on the last line): . 88888 .8888 So protect all accesses to 'func_table' (and func_buf) by preexisting 'func_buf_lock'. It is easy in 'k_fn' handler as 'puts_queue' is expected not to sleep. On the other hand, KDGKBSENT needs a local (atomic) copy of the string because copy_to_user can sleep. Use already allocated, but unused 'kbs->kb_string' for that purpose. Note that the program above needs at least CAP_SYS_TTY_CONFIG. This depends on the previous patch and on the func_buf_lock lock added in commit46ca3f735f
(tty/vt: fix write/write race in ioctl(KDSKBSENT) handler) in 5.2. Likely fixes CVE-2020-25656. Cc: <stable@vger.kernel.org> Reported-by: Minh Yuan <yuanmingbuaa@gmail.com> Signed-off-by: Jiri Slaby <jslaby@suse.cz> Link: https://lore.kernel.org/r/20201019085517.10176-2-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
parent
eb4c460e2e
commit
87d398f348
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@ -742,8 +742,13 @@ static void k_fn(struct vc_data *vc, unsigned char value, char up_flag)
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return;
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return;
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if ((unsigned)value < ARRAY_SIZE(func_table)) {
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if ((unsigned)value < ARRAY_SIZE(func_table)) {
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unsigned long flags;
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spin_lock_irqsave(&func_buf_lock, flags);
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if (func_table[value])
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if (func_table[value])
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puts_queue(vc, func_table[value]);
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puts_queue(vc, func_table[value]);
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spin_unlock_irqrestore(&func_buf_lock, flags);
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} else
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} else
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pr_err("k_fn called with value=%d\n", value);
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pr_err("k_fn called with value=%d\n", value);
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}
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}
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@ -1990,7 +1995,7 @@ out:
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#undef s
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#undef s
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#undef v
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#undef v
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/* FIXME: This one needs untangling and locking */
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/* FIXME: This one needs untangling */
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int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
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int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
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{
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{
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struct kbsentry *kbs;
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struct kbsentry *kbs;
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@ -2022,10 +2027,14 @@ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
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switch (cmd) {
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switch (cmd) {
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case KDGKBSENT: {
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case KDGKBSENT: {
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/* size should have been a struct member */
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/* size should have been a struct member */
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unsigned char *from = func_table[i] ? : "";
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ssize_t len = sizeof(user_kdgkb->kb_string);
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ret = copy_to_user(user_kdgkb->kb_string, from,
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spin_lock_irqsave(&func_buf_lock, flags);
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strlen(from) + 1) ? -EFAULT : 0;
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len = strlcpy(kbs->kb_string, func_table[i] ? : "", len);
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spin_unlock_irqrestore(&func_buf_lock, flags);
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ret = copy_to_user(user_kdgkb->kb_string, kbs->kb_string,
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len + 1) ? -EFAULT : 0;
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goto reterr;
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goto reterr;
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}
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}
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