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hlinnakahlinnaka
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Do stack-depth checking in all postmaster children.
We used to only initialize the stack base pointer when starting up a regular backend, not in other processes. In particular, autovacuum workers can run arbitrary user code, and without stack-depth checking, infinite recursion in e.g an index expression will bring down the whole cluster. The comment about PL/Java using set_stack_base() is not yet true. As the code stands, PL/java still modifies the stack_base_ptr variable directly. However, it's been discussed in the PL/Java mailing list that it should be changed to use the function, because PL/Java is currently oblivious to the register stack used on Itanium. There's another issues with PL/Java, namely that the stack base pointer it sets is not really the base of the stack, it could be something close to the bottom of the stack. That's a separate issue that might need some further changes to this code, but that's a different story. Backpatch to all supported releases.
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lines changed

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‎src/backend/postmaster/postmaster.c

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -946,6 +946,11 @@ PostmasterMain(int argc, char *argv[])
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*/
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set_max_safe_fds();
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/*
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* Set reference point for stack-depth checking.
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*/
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set_stack_base();
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/*
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* Initialize the list of active backends.
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*/
@@ -3944,6 +3949,11 @@ SubPostmasterMain(int argc, char *argv[])
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memset(&port, 0, sizeof(Port));
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read_backend_variables(argv[2], &port);
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/*
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* Set reference point for stack-depth checking
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*/
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set_stack_base();
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/*
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* Set up memory area for GSS information. Mirrors the code in ConnCreate
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* for the non-exec case.

‎src/backend/tcop/postgres.c

Lines changed: 53 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -113,8 +113,10 @@ int PostAuthDelay = 0;
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static long max_stack_depth_bytes = 100 * 1024L;
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/*
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* Stack base pointer -- initialized by PostgresMain. This is not static
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* so that PL/Java can modify it.
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* Stack base pointer -- initialized by PostmasterMain and inherited by
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* subprocesses. This is not static because old versions of PL/Java modify
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* it directly. Newer versions use set_stack_base(), but we want to stay
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* binary-compatible for the time being.
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*/
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char *stack_base_ptr = NULL;
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@@ -3024,6 +3026,53 @@ ia64_get_bsp(void)
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#endif /* IA64 */
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/*
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* set_stack_base: set up reference point for stack depth checking
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*
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* Returns the old reference point, if any.
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*/
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pg_stack_base_t
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set_stack_base(void)
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{
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char stack_base;
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pg_stack_base_t old;
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#if defined(__ia64__) || defined(__ia64)
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old.stack_base_ptr = stack_base_ptr;
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old.register_stack_base_ptr = register_stack_base_ptr;
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#else
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old = stack_base_ptr;
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#endif
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/* Set up reference point for stack depth checking */
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stack_base_ptr = &stack_base;
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#if defined(__ia64__) || defined(__ia64)
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register_stack_base_ptr = ia64_get_bsp();
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#endif
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return old;
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}
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/*
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* restore_stack_base: restore reference point for stack depth checking
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*
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* This can be used after set_stack_base() to restore the old value. This
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* is currently only used in PL/Java. When PL/Java calls a backend function
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* from different thread, the thread's stack is at a different location than
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* the main thread's stack, so it sets the base pointer before the call, and
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* restores it afterwards.
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*/
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void
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restore_stack_base(pg_stack_base_t base)
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{
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#if defined(__ia64__) || defined(__ia64)
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stack_base_ptr = base.stack_base_ptr;
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register_stack_base_ptr = base.register_stack_base_ptr;
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#else
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stack_base_ptr = base;
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#endif
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}
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/*
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* check_stack_depth: check for excessively deep recursion
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*
@@ -3039,7 +3088,7 @@ check_stack_depth(void)
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long stack_depth;
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/*
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* Compute distance from PostgresMain's local variables to my own
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* Compute distance from reference point to to my local variables
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*/
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stack_depth = (long) (stack_base_ptr - &stack_top_loc);
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@@ -3469,7 +3518,6 @@ PostgresMain(int argc, char *argv[], const char *username)
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{
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const char *dbname;
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int firstchar;
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char stack_base;
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StringInfoData input_message;
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sigjmp_buf local_sigjmp_buf;
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volatile bool send_ready_for_query = true;
@@ -3496,10 +3544,7 @@ PostgresMain(int argc, char *argv[], const char *username)
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SetProcessingMode(InitProcessing);
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/* Set up reference point for stack depth checking */
3499-
stack_base_ptr = &stack_base;
3500-
#if defined(__ia64__) || defined(__ia64)
3501-
register_stack_base_ptr = ia64_get_bsp();
3502-
#endif
3547+
set_stack_base();
35033548

35043549
/* Compute paths, if we didn't inherit them from postmaster */
35053550
if (my_exec_path[0] == '\0')

‎src/include/miscadmin.h

Lines changed: 13 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -234,6 +234,19 @@ extern bool VacuumCostActive;
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/* in tcop/postgres.c */
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#if defined(__ia64__) || defined(__ia64)
239+
typedef struct
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{
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char *stack_base_ptr;
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char *register_stack_base_ptr;
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} pg_stack_base_t;
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#else
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typedef char *pg_stack_base_t;
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#endif
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extern pg_stack_base_t set_stack_base(void);
249+
extern void restore_stack_base(pg_stack_base_t base);
237250
extern void check_stack_depth(void);
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/* in tcop/utility.c */

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