[PATCH net] tun: prevent negative ifindex

[Eric Dumazet]

After commit 956db0a13b47 ("net: warn about attempts to register
negative ifindex") syzbot is able to trigger the following splat.

Negative ifindex are not supported.

WARNING: CPU: 1 PID: 6003 at net/core/dev.c:9596 dev_index_reserve+0x104/0x210
Modules linked in:
CPU: 1 PID: 6003 Comm: syz-executor926 Not tainted 6.6.0-rc4-syzkaller-g19af4a4ed414 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/06/2023
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : dev_index_reserve+0x104/0x210
lr : dev_index_reserve+0x100/0x210
sp : ffff800096a878e0
x29: ffff800096a87930 x28: ffff0000d04380d0 x27: ffff0000d04380f8
x26: ffff0000d04380f0 x25: 1ffff00012d50f20 x24: 1ffff00012d50f1c
x23: dfff800000000000 x22: ffff8000929c21c0 x21: 00000000ffffffea
x20: ffff0000d04380e0 x19: ffff800096a87900 x18: ffff800096a874c0
x17: ffff800084df5008 x16: ffff80008051f9c4 x15: 0000000000000001
x14: 1fffe0001a087198 x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
x8 : ffff0000d41c9bc0 x7 : 0000000000000000 x6 : 0000000000000000
x5 : ffff800091763d88 x4 : 0000000000000000 x3 : ffff800084e04748
x2 : 0000000000000001 x1 : 00000000fead71c7 x0 : 0000000000000000
Call trace:
dev_index_reserve+0x104/0x210
register_netdevice+0x598/0x1074 net/core/dev.c:10084
tun_set_iff+0x630/0xb0c drivers/net/tun.c:2850
__tun_chr_ioctl+0x788/0x2af8 drivers/net/tun.c:3118
tun_chr_ioctl+0x38/0x4c drivers/net/tun.c:3403
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:871 [inline]
__se_sys_ioctl fs/ioctl.c:857 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:857
__invoke_syscall arch/arm64/kernel/syscall.c:37 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:51
el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:136
do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:155
el0_svc+0x58/0x16c arch/arm64/kernel/entry-common.c:678
el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:696
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:595
irq event stamp: 11348
hardirqs last enabled at (11347): [<ffff80008a716574>] __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:151 [inline]
hardirqs last enabled at (11347): [<ffff80008a716574>] _raw_spin_unlock_irqrestore+0x38/0x98 kernel/locking/spinlock.c:194
hardirqs last disabled at (11348): [<ffff80008a627820>] el1_dbg+0x24/0x80 arch/arm64/kernel/entry-common.c:436
softirqs last enabled at (11138): [<ffff8000887ca53c>] spin_unlock_bh include/linux/spinlock.h:396 [inline]
softirqs last enabled at (11138): [<ffff8000887ca53c>] release_sock+0x15c/0x1b0 net/core/sock.c:3531
softirqs last disabled at (11136): [<ffff8000887ca41c>] spin_lock_bh include/linux/spinlock.h:356 [inline]
softirqs last disabled at (11136): [<ffff8000887ca41c>] release_sock+0x3c/0x1b0 net/core/sock.c:3518

Fixes: fb7589a16216 ("tun: Add ability to create tun device with given index")
Reported-by: syzbot <syzk...@googlegroups.com>
Signed-off-by: Eric Dumazet <edum...@google.com>
---
drivers/net/tun.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 89ab9efe522c30bd167d690f60c6b18fc29680a5..afa5497f7c35c3ab5682e66440afc8a888d14414 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -3073,10 +3073,11 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
struct net *net = sock_net(&tfile->sk);
struct tun_struct *tun;
void __user* argp = (void __user*)arg;
- unsigned int ifindex, carrier;
+ unsigned int carrier;
struct ifreq ifr;
kuid_t owner;
kgid_t group;
+ int ifindex;
int sndbuf;
int vnet_hdr_sz;
int le;
@@ -3132,7 +3133,9 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
ret = -EFAULT;
if (copy_from_user(&ifindex, argp, sizeof(ifindex)))
goto unlock;
-
+ ret = -EINVAL;
+ if (ifindex < 0)
+ goto unlock;
ret = 0;
tfile->ifindex = ifindex;
goto unlock;
--
2.42.0.655.g421f12c284-goog

[Stephen Hemminger]

On Mon, 16 Oct 2023 18:08:51 +0000
Eric Dumazet <edum...@google.com> wrote:

> + ret = -EINVAL;
> + if (ifindex < 0)
> + goto unlock;

Shouldn't this be <= 0 since 0 is not a valid ifindex.
Zero ifindex is used as a sentinel in some API's

For example: if_nametoindex() returns 0 if name is not found.

[Eric Dumazet]

Setting tfile->ifindex to zero should be a NOP ?

This means dev_index_reserve() will allocate a ifindex for us.

Not sure we want to prevent something that was working properly in the past.

[Stephen Hemminger]

On Mon, 16 Oct 2023 21:42:10 +0200
Eric Dumazet <edum...@google.com> wrote:

> Setting tfile->ifindex to zero should be a NOP ?
>
> This means dev_index_reserve() will allocate a ifindex for us.
>
> Not sure we want to prevent something that was working properly in the past.

That makes sense. did not read ahead to see what happens

[Willem de Bruijn]

Reviewed-by: Willem de Bruijn <wil...@google.com>

[Jason Wang]

Acked-by: Jason Wang <jaso...@redhat.com>

Thanks

>
>

[patchwork-b...@kernel.org]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <ku...@kernel.org>:

> [...]

Here is the summary with links:
- [net] tun: prevent negative ifindex
https://git.kernel.org/netdev/net/c/cbfbfe3aee71

You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

[Greg Kroah-Hartman]

6.5-stable review patch. If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edum...@google.com>

commit cbfbfe3aee718dc4c3c837f5d2463170ee59d78c upstream.

Fixes: fb7589a16216 ("tun: Add ability to create tun device with given index")
Reported-by: syzbot <syzk...@googlegroups.com>
Signed-off-by: Eric Dumazet <edum...@google.com>
Reviewed-by: Willem de Bruijn <wil...@google.com>
Acked-by: Jason Wang <jaso...@redhat.com>

Link: https://lore.kernel.org/r/20231016180851.3...@google.com
Signed-off-by: Jakub Kicinski <ku...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
drivers/net/tun.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -3068,10 +3068,11 @@ static long __tun_chr_ioctl(struct file

struct net *net = sock_net(&tfile->sk);
struct tun_struct *tun;
void __user* argp = (void __user*)arg;
- unsigned int ifindex, carrier;
+ unsigned int carrier;
struct ifreq ifr;
kuid_t owner;
kgid_t group;
+ int ifindex;
int sndbuf;
int vnet_hdr_sz;
int le;

@@ -3127,7 +3128,9 @@ static long __tun_chr_ioctl(struct file

ret = -EFAULT;
if (copy_from_user(&ifindex, argp, sizeof(ifindex)))
goto unlock;
-

+ ret = -EINVAL;
+ if (ifindex < 0)
+ goto unlock;

[Greg Kroah-Hartman]

6.1-stable review patch. If anyone has any objections, please let me know.

@@ -3056,10 +3056,11 @@ static long __tun_chr_ioctl(struct file

struct net *net = sock_net(&tfile->sk);
struct tun_struct *tun;
void __user* argp = (void __user*)arg;
- unsigned int ifindex, carrier;
+ unsigned int carrier;
struct ifreq ifr;
kuid_t owner;
kgid_t group;
+ int ifindex;
int sndbuf;
int vnet_hdr_sz;
int le;

@@ -3115,7 +3116,9 @@ static long __tun_chr_ioctl(struct file

[Greg Kroah-Hartman]

5.4-stable review patch. If anyone has any objections, please let me know.

@@ -3134,10 +3134,11 @@ static long __tun_chr_ioctl(struct file

struct net *net = sock_net(&tfile->sk);
struct tun_struct *tun;
void __user* argp = (void __user*)arg;
- unsigned int ifindex, carrier;
+ unsigned int carrier;
struct ifreq ifr;
kuid_t owner;
kgid_t group;
+ int ifindex;
int sndbuf;
int vnet_hdr_sz;
int le;

@@ -3194,7 +3195,9 @@ static long __tun_chr_ioctl(struct file

[Greg Kroah-Hartman]

5.15-stable review patch. If anyone has any objections, please let me know.

@@ -3010,10 +3010,11 @@ static long __tun_chr_ioctl(struct file

struct net *net = sock_net(&tfile->sk);
struct tun_struct *tun;
void __user* argp = (void __user*)arg;
- unsigned int ifindex, carrier;
+ unsigned int carrier;
struct ifreq ifr;
kuid_t owner;
kgid_t group;
+ int ifindex;
int sndbuf;
int vnet_hdr_sz;
int le;

@@ -3069,7 +3070,9 @@ static long __tun_chr_ioctl(struct file

[Greg Kroah-Hartman]

5.10-stable review patch. If anyone has any objections, please let me know.

@@ -3064,10 +3064,11 @@ static long __tun_chr_ioctl(struct file

struct net *net = sock_net(&tfile->sk);
struct tun_struct *tun;
void __user* argp = (void __user*)arg;
- unsigned int ifindex, carrier;
+ unsigned int carrier;
struct ifreq ifr;
kuid_t owner;
kgid_t group;
+ int ifindex;
int sndbuf;
int vnet_hdr_sz;
int le;

@@ -3124,7 +3125,9 @@ static long __tun_chr_ioctl(struct file