CVE-2021-46912: In the Linux kernel, the following vulnerability has been resolved: net: Make tcp_allowed_congestion_control readonly in non-init netns Currently…

PriorityP420medium5.5CVSS 3.1

AVLACLPRLUINSUCNINAH

EPSS

0.23%

14.2th percentile

In the Linux kernel, the following vulnerability has been resolved: net: Make tcp_allowed_congestion_control readonly in non-init netns Currently, tcp_allowed_congestion_control is global and writable; writing to it in any net namespace will leak into all other net namespaces. tcp_available_congestion_control and tcp_allowed_congestion_control are the only sysctls in ipv4_net_table (the per-netns sysctl table) with a NULL data pointer; their handlers (proc_tcp_available_congestion_control and proc_allowed_congestion_control) have no other way of referencing a struct net. Thus, they operate globally. Because ipv4_net_table does not use designated initializers, there is no easy way to fix up this one "bad" table entry. However, the data pointer updating logic shouldn't be applied to NULL pointers anyway, so we instead force these entries to be read-only. These sysctls used to exist in ipv4_table (init-net only), but they were moved to the per-net ipv4_net_table, presumably without realizing that tcp_allowed_congestion_control was writable and thus introduced a leak. Because the intent of that commit was only to know (i.e. read) "which congestion algorithms are available or allowed", this read-only solution should be sufficient. The logic added in recent commit 31c4d2f160eb: ("net: Ensure net namespace isolation of sysctls") does not and cannot check for NULL data pointers, because other table entries (e.g. /proc/sys/net/netfilter/nf_log/) have .data=NULL but use other methods (.extra2) to access the struct net.

Affected

11 ranges

Vendor	Product	Version range	Fixed in
debian	linux	< linux 5.10.38-1 (bookworm)	linux 5.10.38-1 (bookworm)
linux	linux	—	—
linux	linux	>= 9cb8e048e5d93825ec5e8dfb5b8df4987ea25745 < 35d7491e2f77ce480097cabcaf93ed409e916e12	35d7491e2f77ce480097cabcaf93ed409e916e12
linux	linux	>= 9cb8e048e5d93825ec5e8dfb5b8df4987ea25745 < 1ccdf1bed140820240e383ba0accc474ffc7f006	1ccdf1bed140820240e383ba0accc474ffc7f006
linux	linux	>= 9cb8e048e5d93825ec5e8dfb5b8df4987ea25745 < 97684f0970f6e112926de631fdd98d9693c7e5c1	97684f0970f6e112926de631fdd98d9693c7e5c1
linux	linux_kernel	>= 0 < 5.10.38-1	5.10.38-1
linux	linux_kernel	>= 0 < 5.10.38-1	5.10.38-1
linux	linux_kernel	>= 0 < 5.10.38-1	5.10.38-1
linux	linux_kernel	>= 0 < 5.10.38-1	5.10.38-1
linux	linux_kernel	>= 5.11.0 < 5.11.16	5.11.16
linux	linux_kernel	>= 5.7.0 < 5.10.32	5.10.32

CVSS provenance

nvdv3.15.5MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

osv5.5MEDIUM

vendor_debian5.5MEDIUM

vendor_redhat5.5MEDIUM

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