runtime, cgo: cgo call to setgid hangs on GNU/Linux #3871
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This issue was closed by revision b9e051e. Status changed to Fixed. |
aclements
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Dec 23, 2014
These signals are used by glibc to broadcast setuid/setgid to all threads and to send pthread cancellations. Unlike other signals, the Go runtime does not intercept these because they must invoke the libc handlers (see issues #3871 and #6997). However, because 1) these signals may be issued asynchronously by a thread running C code to another thread running Go code and 2) glibc does not set SA_ONSTACK for its handlers, glibc's signal handler may be run on a Go stack. Signal frames range from 1.5K on amd64 to many kilobytes on ppc64, so this may overflow the Go stack and corrupt heap (or other stack) data. Fix this by ensuring that these signal handlers have the SA_ONSTACK flag (but not otherwise taking over the handler). This has been a problem since Go 1.1, but it's likely that people haven't encountered it because it only affects setuid/setgid and pthread_cancel. Fixes #9600. Change-Id: I6cf5f5c2d3aa48998d632f61f1ddc2778dcfd300 Reviewed-on: https://go-review.googlesource.com/1887 Reviewed-by: Ian Lance Taylor <[email protected]>
ianlancetaylor
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May 11, 2015
««« backport bfa4e1f1027f runtime: ignore signal 33 == SIGSETXID on GNU/Linux When a cgo program calls setuid, setgid, etc., the GNU/Linux pthread library sends signal SIGSETXID to each thread to tell it to update its UID info. If Go is permitted to intercept the default SIGSETXID signal handler, the program will hang. This patch tells the runtime package to not try to intercept SIGSETXID on GNU/Linux. This will be odd if a Go program wants to try to use that signal, but it means that cgo programs that call setuid, etc., won't hang. Fixes #3871. R=rsc, r, minux.ma, bradfitz CC=golang-dev https://golang.org/cl/6455050 »»»
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This program hangs on GNU/Linux. package main /* #include <sys/types.h> #include <unistd.h> */ import "C" import "fmt" func main() { i, errno := C.setgid(1) fmt.Println(i, errno) } The problem is that when a threaded program calls setgid, the pthreads library sends a SIGSETXID signal to each thread, and waits for the thread to acknowledge it. The Go runtime overrides the default signal handler with a Go-specific one. Since the os/signal package is not imported, the Go-specific signal handler simply ignores SIGSETXID. This means that the acknowledgement is never sent, and the program hangs.The text was updated successfully, but these errors were encountered: