[uclibc-ng-devel] [PATCH] Fix infinite loop when fopencookie custom write returns 0 on error

The man page for fopencookie prescribes that custom write functions should return 0 on error (and should definitely not return a negative value) [1]. However, the uClibc implementation expects a negative return value in case of an error (libc/stdio/_WRITE.c). If the write function returns 0 on error, we drop into an infinite loop if the error persists. This patch wraps the user supplied write function such that a 0 return value is converted to -1. errno is first set to EAGAIN such that if the custom write function does not set errno in case of error, this is treated as a "soft" error. Custom write functions that cater towards uClibc and _do_ return a negative value are not affected. If no custom write function is supplied, set errno to EINVAL such that this condition is treated as a "hard" error. Previously the behaviour depended on whether the last error before the write happened to be a "hard" or a "soft" error. [1] http://git.kernel.org/cgit/docs/man-pages/man-pages.git/tree/man3/fopencook… Signed-off-by: Jan Vangorp <jan.vangorp_ext(a)softathome.com> --- libc/stdio/_stdio.h | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/libc/stdio/_stdio.h b/libc/stdio/_stdio.h index 310510d..727e331 100644 --- a/libc/stdio/_stdio.h +++ b/libc/stdio/_stdio.h @@ -110,6 +110,18 @@ do { \ cfile->__gcs.NAME(cfile->__cookie, ##ARGS); \ } +#define __STDIO_STREAM_CUSTOM_WRITE_FUNC(S, ARGS...) \ + if (__STDIO_STREAM_IS_CUSTOM((S))) { \ + _IO_cookie_file_t *cfile = (_IO_cookie_file_t *) (S); \ + if (cfile->__gcs.write == NULL) { \ + __set_errno(EINVAL); \ + return -1; \ + } \ + __set_errno(EAGAIN); \ + ssize_t w = cfile->__gcs.write(cfile->__cookie, ##ARGS); \ + return (w == 0 ? -1 : w); \ + } + typedef struct { struct __STDIO_FILE_STRUCT __fp; void *__cookie; @@ -121,6 +133,7 @@ typedef struct { #undef __STDIO_STREAM_GLIBC_CUSTOM_FILEDES #define __STDIO_STREAM_IS_CUSTOM(S) (0) #define __STDIO_STREAM_CUSTOM_IO_FUNC(S, NAME, RC, ARGS...) +#define __STDIO_STREAM_CUSTOM_WRITE_FUNC(S, ARGS...) #endif /* __UCLIBC_HAS_GLIBC_CUSTOM_STREAMS__ */ @@ -135,7 +148,7 @@ static inline ssize_t __READ(FILE *stream, char *buf, size_t bufsize) static inline ssize_t __WRITE(FILE *stream, const char *buf, size_t bufsize) { - __STDIO_STREAM_CUSTOM_IO_FUNC(stream, write, -1, buf, bufsize); + __STDIO_STREAM_CUSTOM_WRITE_FUNC(stream, buf, bufsize); return write(stream->__filedes, buf, bufsize); } -- 1.9.1