This is a note to let you know that I've just added the patch titled

debugfs: Return -EPERM when locked down

to my driver-core git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git in the driver-core-next branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release during the merge window.

If you have any questions about this process, please let me know.

From a37f4958f7b63d2b3cd17a76151fdfc29ce1da5f Mon Sep 17 00:00:00 2001

From: Eric Snowberg eric.snowberg@oracle.com Date: Sat, 7 Dec 2019 11:16:03 -0500 Subject: debugfs: Return -EPERM when locked down

When lockdown is enabled, debugfs_is_locked_down returns 1. It will then trigger the following:

WARNING: CPU: 48 PID: 3747 CPU: 48 PID: 3743 Comm: bash Not tainted 5.4.0-1946.x86_64 #1 Hardware name: Oracle Corporation ORACLE SERVER X7-2/ASM, MB, X7-2, BIOS 41060400 05/20/2019 RIP: 0010:do_dentry_open+0x343/0x3a0 Code: 00 40 08 00 45 31 ff 48 c7 43 28 40 5b e7 89 e9 02 ff ff ff 48 8b 53 28 4c 8b 72 70 4d 85 f6 0f 84 10 fe ff ff e9 f5 fd ff ff <0f> 0b 41 bf ea ff ff ff e9 3b ff ff ff 41 bf e6 ff ff ff e9 b4 fe RSP: 0018:ffffb8740dde7ca0 EFLAGS: 00010202 RAX: ffffffff89e88a40 RBX: ffff928c8e6b6f00 RCX: 0000000000000000 RDX: 0000000000000000 RSI: ffff928dbfd97778 RDI: ffff9285cff685c0 RBP: ffffb8740dde7cc8 R08: 0000000000000821 R09: 0000000000000030 R10: 0000000000000057 R11: ffffb8740dde7a98 R12: ffff926ec781c900 R13: ffff928c8e6b6f10 R14: ffffffff8936e190 R15: 0000000000000001 FS: 00007f45f6777740(0000) GS:ffff928dbfd80000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fff95e0d5d8 CR3: 0000001ece562006 CR4: 00000000007606e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: vfs_open+0x2d/0x30 path_openat+0x2d4/0x1680 ? tty_mode_ioctl+0x298/0x4c0 do_filp_open+0x93/0x100 ? strncpy_from_user+0x57/0x1b0 ? __alloc_fd+0x46/0x150 do_sys_open+0x182/0x230 __x64_sys_openat+0x20/0x30 do_syscall_64+0x60/0x1b0 entry_SYSCALL_64_after_hwframe+0x170/0x1d5 RIP: 0033:0x7f45f5e5ce02 Code: 25 00 00 41 00 3d 00 00 41 00 74 4c 48 8d 05 25 59 2d 00 8b 00 85 c0 75 6d 89 f2 b8 01 01 00 00 48 89 fe bf 9c ff ff ff 0f 05 <48> 3d 00 f0 ff ff 0f 87 a2 00 00 00 48 8b 4c 24 28 64 48 33 0c 25 RSP: 002b:00007fff95e0d2e0 EFLAGS: 00000246 ORIG_RAX: 0000000000000101 RAX: ffffffffffffffda RBX: 0000561178c069b0 RCX: 00007f45f5e5ce02 RDX: 0000000000000241 RSI: 0000561178c08800 RDI: 00000000ffffff9c RBP: 00007fff95e0d3e0 R08: 0000000000000020 R09: 0000000000000005 R10: 00000000000001b6 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000003 R14: 0000000000000001 R15: 0000561178c08800

Change the return type to int and return -EPERM when lockdown is enabled to remove the warning above. Also rename debugfs_is_locked_down to debugfs_locked_down to make it sound less like it returns a boolean.

Fixes: 5496197f9b08 ("debugfs: Restrict debugfs when the kernel is locked down") Signed-off-by: Eric Snowberg eric.snowberg@oracle.com Reviewed-by: Matthew Wilcox (Oracle) willy@infradead.org Cc: stable stable@vger.kernel.org Acked-by: James Morris jamorris@linux.microsoft.com Link: https://lore.kernel.org/r/20191207161603.35907-1-eric.snowberg@oracle.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/debugfs/file.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c index 8be46add9105..634b09d18b77 100644 --- a/fs/debugfs/file.c +++ b/fs/debugfs/file.c @@ -142,18 +142,21 @@ EXPORT_SYMBOL_GPL(debugfs_file_put); * We also need to exclude any file that has ways to write or alter it as root * can bypass the permissions check. */ -static bool debugfs_is_locked_down(struct inode *inode, - struct file *filp, - const struct file_operations *real_fops) +static int debugfs_locked_down(struct inode *inode, + struct file *filp, + const struct file_operations *real_fops) { if ((inode->i_mode & 07777) == 0444 && !(filp->f_mode & FMODE_WRITE) && !real_fops->unlocked_ioctl && !real_fops->compat_ioctl && !real_fops->mmap) - return false; + return 0;

- return security_locked_down(LOCKDOWN_DEBUGFS); + if (security_locked_down(LOCKDOWN_DEBUGFS)) + return -EPERM; + + return 0; }

static int open_proxy_open(struct inode *inode, struct file *filp) @@ -168,7 +171,7 @@ static int open_proxy_open(struct inode *inode, struct file *filp)

real_fops = debugfs_real_fops(filp);

- r = debugfs_is_locked_down(inode, filp, real_fops); + r = debugfs_locked_down(inode, filp, real_fops); if (r) goto out;

@@ -298,7 +301,7 @@ static int full_proxy_open(struct inode *inode, struct file *filp)

real_fops = debugfs_real_fops(filp);

- r = debugfs_is_locked_down(inode, filp, real_fops); + r = debugfs_locked_down(inode, filp, real_fops); if (r) goto out;