ptrace: slightly saner 'get_dumpable()' logic

Description

In the Linux kernel, the following vulnerability has been resolved: ptrace: slightly saner 'get_dumpable()' logic The 'dumpability' of a task is fundamentally about the memory image of the task - the concept comes from whether it can core dump or not - and makes no sense when you don't have an associated mm. And almost all users do in fact use it only for the case where the task has a mm pointer. But we have one odd special case: ptrace_may_access() uses 'dumpable' to check various other things entirely independently of the MM (typically explicitly using flags like PTRACE_MODE_READ_FSCREDS). Including for threads that no longer have a VM (and maybe never did, like most kernel threads). It's not what this flag was designed for, but it is what it is. The ptrace code does check that the uid/gid matches, so you do have to be uid-0 to see kernel thread details, but this means that the traditional "drop capabilities" model doesn't make any difference for this all. Make it all make a *bit* more sense by saying that if you don't have a MM pointer, we'll use a cached "last dumpability" flag if the thread ever had a MM (it will be zero for kernel threads since it is never set), and require a proper CAP_SYS_PTRACE capability to override.

Affected Products

Also Affects

Downstream vendors/products affected by this vulnerability

References

• https://git.kernel.org/stable/c/93d4ba49d18e3d7fb41a9927c2d0cca5e9dfefd6
• https://git.kernel.org/stable/c/15b828a46f305ae9f05a7c16914b3ce273474205
• https://git.kernel.org/stable/c/4709234fd1b95136ceb789f639b1e7ea5de1b181
• https://git.kernel.org/stable/c/8f907d345bae8f4b3f004c5abc56bf2dfb851ea7
• https://git.kernel.org/stable/c/6e5b51e74a40d377bcd3081dd33fbaa0e1aa7e3d
• https://git.kernel.org/stable/c/2a93a4fac7b6051d3be7cd1b015fe7320cd0404d
• https://git.kernel.org/stable/c/01363cb3fbd0238ffdeb09f53e9039c9edf8a730
• https://git.kernel.org/stable/c/31e62c2ebbfdc3fe3dbdf5e02c92a9dc67087a3a

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