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[71.206.142.238]) by smtp.gmail.com with ESMTPSA id l16-20020a056214029000b0062168714c8fsm2058694qvv.120.2023.05.22.09.55.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 May 2023 09:55:32 -0700 (PDT) From: Joe Simmons-Talbott To: libc-alpha@sourceware.org Cc: Joe Simmons-Talbott Subject: [PATCH v2] vfprintf-internal: Get rid of alloca. Date: Mon, 22 May 2023 12:55:29 -0400 Message-Id: <20230522165529.238596-1-josimmon@redhat.com> X-Mailer: git-send-email 2.40.0 MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="US-ASCII"; x-default=true X-Spam-Status: No, score=-12.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Avoid potential stack overflow from unbounded alloca. Use the existing scratch_buffer instead. --- Changes to v1: * fix 32bit builds. * ensure we have enough space in the scratch buffer before using it. stdio-common/vfprintf-internal.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) diff --git a/stdio-common/vfprintf-internal.c b/stdio-common/vfprintf-internal.c index c76c06e49b..c05fc149d1 100644 --- a/stdio-common/vfprintf-internal.c +++ b/stdio-common/vfprintf-internal.c @@ -1066,6 +1066,8 @@ printf_positional (struct Xprintf_buffer * buf, const CHAR_T *format, union printf_arg *args_value; int *args_size; int *args_type; + int *args_pa_user; + size_t args_pa_user_offset; { /* Calculate total size needed to represent a single argument across all three argument-related arrays. */ @@ -1082,6 +1084,7 @@ printf_positional (struct Xprintf_buffer * buf, const CHAR_T *format, now. */ args_size = &args_value[nargs].pa_int; args_type = &args_size[nargs]; + args_pa_user = &args_type[nargs]; memset (args_type, (mode_flags & PRINTF_FORTIFY) != 0 ? '\xff' : '\0', nargs * sizeof (*args_type)); } @@ -1171,7 +1174,25 @@ printf_positional (struct Xprintf_buffer * buf, const CHAR_T *format, else if (__glibc_unlikely (__printf_va_arg_table != NULL) && __printf_va_arg_table[args_type[cnt] - PA_LAST] != NULL) { - args_value[cnt].pa_user = alloca (args_size[cnt]); + if (args_pa_user + args_size[cnt] > + (int *) &argsbuf + argsbuf.length) + { + args_pa_user_offset = args_pa_user - &args_type[nargs]; + if (!scratch_buffer_grow_preserve (&argsbuf)) + { + Xprintf_buffer_mark_failed (buf); + goto all_done; + } + args_value = argsbuf.data; + /* Set up the remaining two arrays to each point past the end of + the prior array, since space for all three has been allocated + now. */ + args_size = &args_value[nargs].pa_int; + args_type = &args_size[nargs]; + args_pa_user = &args_type[nargs] + args_pa_user_offset; + } + args_value[cnt].pa_user = args_pa_user; + args_pa_user += args_size[cnt]; (*__printf_va_arg_table[args_type[cnt] - PA_LAST]) (args_value[cnt].pa_user, ap_savep); } -- 2.39.2