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core: ppp: use a different unit for each activation

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We can't tell pppd to create an interface with a given name, so we use
the name generated by kernel and rename the interface afterwards. A
race condition can happen during the rename: NM receives the interface
name from pppd, but in the meantime the interface could be deleted and
another one with that name could appear. In this case we would rename
the wrong interface.

Using a changing unit index, we ensure that interfaces created by NM
don't race with each others. There is still the chance to race with
externally-created interfaces, but I guess this is not easily solvable
since the pppd plugin does not expose the ifindex.

When the specified unit is already in use, the kernel selects another
one.
This commit is contained in:
Beniamino Galvani 2017-07-03 17:01:43 +02:00
parent a7afa9ead7
commit 74bf32ff9a
1 changed files with 10 additions and 0 deletions
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10
src/ppp/nm-ppp-manager.c
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@ -678,6 +678,7 @@ create_pppd_cmd_line (NMPPPManager *self,
const char *pppd_binary = NULL;
NMCmdLine *cmd;
gboolean ppp_debug;
static int unit;
g_return_val_if_fail (setting != NULL, NULL);
@ -842,6 +843,15 @@ create_pppd_cmd_line (NMPPPManager *self,
nm_cmd_line_add_string (cmd, "plugin");
nm_cmd_line_add_string (cmd, NM_PPPD_PLUGIN);
if (pppoe && nm_setting_pppoe_get_parent (pppoe)) {
/* The PPP interface is going to be renamed, so pass a
* different unit each time so that activations don't
* race with each others. */
nm_cmd_line_add_string (cmd, "unit");
nm_cmd_line_add_int (cmd, unit);
unit = unit < G_MAXINT ? unit + 1 : 0;
}
return cmd;
}