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crypto/tls: don't overwrite Config.sessionTicketKeys if already set #15421

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mark-kubacki opened this issue Apr 23, 2016 · 3 comments
Closed

crypto/tls: don't overwrite Config.sessionTicketKeys if already set #15421

mark-kubacki opened this issue Apr 23, 2016 · 3 comments
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@mark-kubacki
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With Go 1.6.2 and earlier and in tls.Config, serverInit() overwrites effects of a prior SetSessionTicketKeys().

Initializing SessionTicketKey to an arbitrary non-null value does not sort this in case of TLS ticket key rotation: SetSessionTicketKeys() could have already been called several times without being allowed to update that lone field because »after [tls.Config has] been passed to a TLS function it must not be modified«.

I expected serverInit() to:

diff --git a/src/crypto/tls/common.go b/src/crypto/tls/common.go
index c68ebfe..94be97e 100644
--- a/src/crypto/tls/common.go
+++ b/src/crypto/tls/common.go
@@ -388,6 +388,9 @@ func (c *Config) serverInit() {
        if c.SessionTicketsDisabled {
                return
        }
+       if len(c.ticketKeys()) > 0 {
+               return
+       }

        alreadySet := false
        for _, b := range c.SessionTicketKey {
@mark-kubacki
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go/src/crypto/tls/common.go

Lines 424 to 435 in 57e459e

func (c *Config) SetSessionTicketKeys(keys [][32]byte) {
if len(keys) == 0 {
panic("tls: keys must have at least one key")
}
newKeys := make([]ticketKey, len(keys))
for i, bytes := range keys {
newKeys[i] = ticketKeyFromBytes(bytes)
}
c.mutex.Lock()
c.sessionTicketKeys = newKeys

go/src/crypto/tls/common.go

Lines 387 to 407 in 57e459e

func (c *Config) serverInit() {
if c.SessionTicketsDisabled {
return
}
alreadySet := false
for _, b := range c.SessionTicketKey {
if b != 0 {
alreadySet = true
break
}
}
if !alreadySet {
if _, err := io.ReadFull(c.rand(), c.SessionTicketKey[:]); err != nil {
c.SessionTicketsDisabled = true
return
}
}
c.sessionTicketKeys = []ticketKey{ticketKeyFromBytes(c.SessionTicketKey)}

mark-kubacki added a commit to caddyserver/caddy that referenced this issue Apr 23, 2016
@mark-kubacki
tls: Prevent Go stdlib from overwriting our very first tls ticket key
25fc0c6 
[1] https://github.com/golang/go/blob/57e459e02b4b01567f92542f92cd9afde209e193/src/crypto/tls/common.go#L424
[2] https://github.com/golang/go/blob/57e459e02b4b01567f92542f92cd9afde209e193/src/crypto/tls/common.go#L392-L407

[2] has overwritten the first tls ticket key on round N=0, that has previously
been written using [1].

Go's stdlib does not use c.sessionTicketKeys≥1 as indicator if those values had
already been set; initializing that lone SessionTicketKey does the job for for
now.
    If c.serverInit() were called in round N+1 all existing tls ticket keys
are being overwritten (in round N<4 except the very first one, of course).
Member variables for tls.Config are read-only by then, so we cannot just keep
updating SessionTicketKey as well.

This has been escalated to upstream with golang/go#15421 here:
golang/go#15421

Thanks to Matthew Holt for the initial report!
mark-kubacki added a commit to caddyserver/caddy that referenced this issue Apr 23, 2016
@mark-kubacki
tls: Prevent Go stdlib from overwriting our very first tls ticket key (…
6f5cff5 
…#785)

[1] https://github.com/golang/go/blob/57e459e02b4b01567f92542f92cd9afde209e193/src/crypto/tls/common.go#L424
[2] https://github.com/golang/go/blob/57e459e02b4b01567f92542f92cd9afde209e193/src/crypto/tls/common.go#L392-L407

[2] has overwritten the first tls ticket key on round N=0, that has previously
been written using [1].

Go's stdlib does not use c.sessionTicketKeys≥1 as indicator if those values had
already been set; initializing that lone SessionTicketKey does the job for for
now.
    If c.serverInit() were called in round N+1 all existing tls ticket keys
would be overwritten (in round N<4 except the very first one, of course).
As member variables of tls.Config are read-only by then, we cannot keep
updating SessionTicketKey as well.

This has been escalated to Go's authors with golang/go#15421 here:
golang/go#15421

Thanks to Matthew Holt for the initial report!
@bradfitz bradfitz changed the title tls: Don't overwerwrite tls.Config.sessionTicketKeys if already set crypto/tls: Don't overwerwrite tls.Config.sessionTicketKeys if already set Apr 23, 2016
@bradfitz bradfitz added this to the Unplanned milestone Apr 23, 2016
@bradfitz bradfitz changed the title crypto/tls: Don't overwerwrite tls.Config.sessionTicketKeys if already set crypto/tls: don't overwrite Config.sessionTicketKeys if already set Apr 23, 2016
@mark-kubacki
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Given that this is a minor bugfix, any chance to see this in Go 1.7 or 1.8?

@bradfitz bradfitz modified the milestones: Go1.8, Unplanned Aug 8, 2016
@gopherbot
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CL https://golang.org/cl/27317 mentions this issue.

@mark-kubacki mark-kubacki mentioned this issue Jan 15, 2017
Closed
@mholt mholt mentioned this issue Jan 15, 2017
Merged
@golang golang locked and limited conversation to collaborators Aug 18, 2017
FiloSottile pushed a commit to FiloSottile/go that referenced this issue Oct 12, 2018
@agl
crypto/tls: don't generate random ticket keys if already set.
2c396d9 
If SetSessionTicketKeys was called on a fresh tls.Config, the configured
keys would be overridden with a random key by serverInit.

Fixes golang#15421.

Change-Id: I5d6cc81fc3e5de4dfa15eb614d102fb886150d1b
Reviewed-on: https://go-review.googlesource.com/27317
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
FiloSottile pushed a commit to FiloSottile/go that referenced this issue Oct 12, 2018
@agl
crypto/tls: don't generate random ticket keys if already set.
251d647 
If SetSessionTicketKeys was called on a fresh tls.Config, the configured
keys would be overridden with a random key by serverInit.

Fixes golang#15421.

Change-Id: I5d6cc81fc3e5de4dfa15eb614d102fb886150d1b
Reviewed-on: https://go-review.googlesource.com/27317
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
@rsc rsc unassigned agl Jun 23, 2022
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