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Commitae33659

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Be more wary about NULL values for GUC string variables.
get_explain_guc_options() crashed if a string GUC marked GUC_EXPLAINhas a NULL boot_val. Nosing around found a couple of other placesthat seemed insufficiently cautious about NULL string values, althoughthose are likely unreachable in practice. Add some commentarydefining the expectations for NULL values of string variables,in hopes of forestalling future additions of more such bugs.Xing Guo, Aleksander Alekseev, Tom LaneDiscussion:https://postgr.es/m/CACpMh+AyDx5YUpPaAgzVwC1d8zfOL4JoD-uyFDnNSa1z0EsDQQ@mail.gmail.com
1 parent2001aab commitae33659

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2 files changed

+20
-2
lines changed

2 files changed

+20
-2
lines changed

‎src/backend/utils/misc/guc.c

Lines changed: 10 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -9950,7 +9950,14 @@ get_explain_guc_options(int *num)
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{
99519951
structconfig_string*lconf= (structconfig_string*)conf;
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9953-
modified= (strcmp(lconf->boot_val,*(lconf->variable))!=0);
9953+
if (lconf->boot_val==NULL&&
9954+
*lconf->variable==NULL)
9955+
modified= false;
9956+
elseif (lconf->boot_val==NULL||
9957+
*lconf->variable==NULL)
9958+
modified= true;
9959+
else
9960+
modified= (strcmp(lconf->boot_val,*(lconf->variable))!=0);
99549961
}
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break;
99569963

@@ -10694,7 +10701,8 @@ write_one_nondefault_variable(FILE *fp, struct config_generic *gconf)
1069410701
{
1069510702
structconfig_string*conf= (structconfig_string*)gconf;
1069610703

10697-
fprintf(fp,"%s",*conf->variable);
10704+
if (*conf->variable)
10705+
fprintf(fp,"%s",*conf->variable);
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}
1069910707
break;
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‎src/include/utils/guc_tables.h

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -227,6 +227,16 @@ struct config_real
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void*reset_extra;
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};
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230+
/*
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* A note about string GUCs: the boot_val is allowed to be NULL, which leads
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* to the reset_val and the actual variable value (*variable) also being NULL.
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* However, there is no way to set a NULL value subsequently using
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* set_config_option or any other GUC API. Also, GUC APIs such as SHOW will
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* display a NULL value as an empty string. Callers that choose to use a NULL
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* boot_val should overwrite the setting later in startup, or else be careful
237+
* that NULL doesn't have semantics that are visibly different from an empty
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* string.
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*/
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structconfig_string
231241
{
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structconfig_genericgen;

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