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proc: add config & param to block forcing mem writes

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[ Upstream commit 41e8149c8892ed1962bd15350b3c3e6e90cba7f4 ]

This adds a Kconfig option and boot param to allow removing
the FOLL_FORCE flag from /proc/pid/mem write calls because
it can be abused.

The traditional forcing behavior is kept as default because
it can break GDB and some other use cases.

Previously we tried a more sophisticated approach allowing
distributions to fine-tune /proc/pid/mem behavior, however
that got NAK-ed by Linus [1], who prefers this simpler
approach with semantics also easier to understand for users.

Link: https://lore.kernel.org/lkml/CAHk-=wiGWLChxYmUA5HrT5aopZrB7_2VTa0NLZcxORgkUe5tEQ@mail.gmail.com/ [1]
Cc: Doug Anderson <[email protected]>
Cc: Jeff Xu <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Christian Brauner <[email protected]>
Suggested-by: Linus Torvalds <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Adrian Ratiu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
This commit is contained in:
Adrian Ratiu 2024-08-02 11:02:25 +03:00 • committed by Greg Kroah-Hartman
commit 299b917594
3 changed files with 102 additions and 1 deletions
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32
security/Kconfig
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@ -19,6 +19,38 @@ config SECURITY_DMESG_RESTRICT
If you are unsure how to answer this question, answer N.
choice
prompt "Allow /proc/pid/mem access override"
default PROC_MEM_ALWAYS_FORCE
help
Traditionally /proc/pid/mem allows users to override memory
permissions for users like ptrace, assuming they have ptrace
capability.
This allows people to limit that - either never override, or
require actual active ptrace attachment.
Defaults to the traditional behavior (for now)
config PROC_MEM_ALWAYS_FORCE
bool "Traditional /proc/pid/mem behavior"
help
This allows /proc/pid/mem accesses to override memory mapping
permissions if you have ptrace access rights.
config PROC_MEM_FORCE_PTRACE
bool "Require active ptrace() use for access override"
help
This allows /proc/pid/mem accesses to override memory mapping
permissions for active ptracers like gdb.
config PROC_MEM_NO_FORCE
bool "Never"
help
Never override memory mapping permissions
endchoice
config SECURITY
bool "Enable different security models"
depends on SYSFS