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f79f4546cf
When in a userns, tasks can't write to certain sysctl files:
(00.009653) 1: Error (sysctl.c:142): Can't open sysctl kernel/hostname: Permission denied
See inline comments for details on affected namespaces.
Mostly for my own education in what is required to port something to be
userns restorable, I ported the sysctl stuff. A potential concern for this
patch is that copying structures with pointers around is kind of gory. I
did it ad-hoc here, but it may be worth inventing some mechanisms to make
it easier, although I'm not sure what exactly that would look like
(potentially re-using some of the protobuf bits; I'll investigate this more
if it looks helpful when doing the cgroup user namespaces port?).
Another issue is that there is not a great way to return non-fd stuff in
memory right now from userns_call; one of the little hacks in this code
would be "simplified" if we invented a way to do this.
v2: coalesce the individual struct sysctl_req requests into one big
sysctl_userns_req that is in a contiguous region of memory so that we
can pass it via userns_call. Hopefully nobody finds my little ascii
diagram too offensive :)
v3: use the fork/setns trick to change the syctl values in the right ns for
IPC/UTS nses; see inline comment for details
v4: only use sysctl_userns_req when actually doing a userns_call.
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
39 lines
887 B
C
39 lines
887 B
C
#ifndef __CR_SYSCTL_H__
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#define __CR_SYSCTL_H__
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struct sysctl_req {
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char *name;
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void *arg;
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int type;
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int flags;
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};
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extern int sysctl_op(struct sysctl_req *req, size_t nr_req, int op, unsigned int ns);
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enum {
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CTL_READ,
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CTL_WRITE,
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};
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#define CTL_SHIFT 4 /* Up to 16 types */
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#define CTL_U32 1 /* Single u32 */
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#define CTL_U64 2 /* Single u64 */
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#define __CTL_U32A 3 /* Array of u32 */
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#define __CTL_U64A 4 /* Array of u64 */
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#define __CTL_STR 5 /* String */
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#define CTL_32 6 /* Single s32 */
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#define CTL_U32A(n) (__CTL_U32A | ((n) << CTL_SHIFT))
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#define CTL_U64A(n) (__CTL_U64A | ((n) << CTL_SHIFT))
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#define CTL_STR(len) (__CTL_STR | ((len) << CTL_SHIFT))
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#define CTL_LEN(t) ((t) >> CTL_SHIFT)
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#define CTL_TYPE(t) ((t) & ((1 << CTL_SHIFT) - 1))
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/*
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* Some entries might be missing mark them as optional.
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*/
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#define CTL_FLAGS_OPTIONAL 1
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#endif /* __CR_SYSCTL_H__ */
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