From e7570f4131a6af9405af7b4fd1c31de807e7cf68 Mon Sep 17 00:00:00 2001 From: Florian Weimer Date: Wed, 16 Dec 2020 15:09:52 +0100 Subject: Replace __libc_multiple_libcs with __libc_initial flag Change sbrk to fail for !__libc_initial (in the generic implementation). As a result, sbrk is (relatively) safe to use for the __libc_initial case (from the main libc). It is therefore no longer necessary to avoid using it in that case (or updating the brk cache), and the __libc_initial flag does not need to be updated as part of dlmopen or static dlopen. As before, direct brk system calls on Linux may lead to memory corruption. Reviewed-by: Adhemerval Zanella --- misc/sbrk.c | 34 ++++++++++++++++++++++++---------- 1 file changed, 24 insertions(+), 10 deletions(-) (limited to 'misc') diff --git a/misc/sbrk.c b/misc/sbrk.c index ba3322fba6..a6929d736d 100644 --- a/misc/sbrk.c +++ b/misc/sbrk.c @@ -16,9 +16,10 @@ . */ #include +#include +#include #include #include -#include /* Defined in brk.c. */ extern void *__curbrk; @@ -30,21 +31,34 @@ extern int __brk (void *addr); void * __sbrk (intptr_t increment) { - void *oldbrk; - - /* If this is not part of the dynamic library or the library is used - via dynamic loading in a statically linked program update - __curbrk from the kernel's brk value. That way two separate - instances of __brk and __sbrk can share the heap, returning - interleaved pieces of it. */ - if (__curbrk == NULL || __libc_multiple_libcs) + /* Controls whether __brk (0) is called to read the brk value from + the kernel. */ + bool update_brk = __curbrk == NULL; + +#if defined (SHARED) && ! IS_IN (rtld) + if (!__libc_initial) + { + if (increment != 0) + { + /* Do not allow changing the brk from an inner libc because + it cannot be synchronized with the outer libc's brk. */ + __set_errno (ENOMEM); + return (void *) -1; + } + /* Querying the kernel's brk value from an inner namespace is + fine. */ + update_brk = true; + } +#endif + + if (update_brk) if (__brk (0) < 0) /* Initialize the break. */ return (void *) -1; if (increment == 0) return __curbrk; - oldbrk = __curbrk; + void *oldbrk = __curbrk; if (increment > 0 ? ((uintptr_t) oldbrk + (uintptr_t) increment < (uintptr_t) oldbrk) : ((uintptr_t) oldbrk < (uintptr_t) -increment)) -- cgit 1.4.1