On Fri, Jan 09, 2015 at 03:20:04PM -0600, Eric W. Biederman wrote: > Rich Felker <dalias@xxxxxxxxxx> writes: > > > On Fri, Jan 09, 2015 at 08:56:26PM +0000, Al Viro wrote: > >> On Fri, Jan 09, 2015 at 03:48:15PM -0500, Rich Felker wrote: > >> > I think this is a case that needs to be fixed, though it's hard. The > >> > normal correct usage for fexecve is to always pass an O_CLOEXEC file > >> > descriptor, and the caller can't really be expected to know whether > >> > the file is a script or not. We discussed workarounds before and one > >> > idea I proposed was having fexecve provide a "one open only" magic > >> > symlink in /proc/self/ to pass to the interpreter. It would behave > >> > like an O_PATH file descriptor magic symlink in /proc/self/fd, but > >> > would automatically cease to exist on the first open (at which point > >> > the interpreter would have a real O_RDONLY file descriptor for the > >> > underlying file). > >> > >> For fsck sake, folks, if you have bloody /proc, you don't need that shite > >> at all! Just do execve on /proc/self/fd/n, and be done with that. > >> > >> The sole excuse for merging that thing in the first place had been > >> "would anybody think of children^Wsclerotic^Whardened environments > >> where they have no /proc at all". > > > > That doesn't work. With O_CLOEXEC, /proc/self/fd/n is already gone at > > the time the interpreter runs, whether you're using fexecveat or > > execve with "/proc/self/fd/n" to implement POSIX fexecve(). That's the > > problem. This breaks the intended idiom for fexecve. > > O_CLOEXEC with a #! intepreter can not work. If the file descriptor is > closed a #! interpreter can not open it. So I don't know why or how > you want that to work but it is nonsense. The why is simple: fexecve always expects a close-on-exec file descriptor. Otherwise the program being executed would need to take a special option telling it to close the spurious fd it inherits. Most programs don't have such an option, and there's no way to do it without application-specific knowledge. The how is difficult, but it can be done. Rich -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
