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authorSimon Marchi <simon.marchi@polymtl.ca>2022-12-15 14:06:25 -0500
committerSimon Marchi <simon.marchi@polymtl.ca>2022-12-15 21:49:29 -0500
commitf8631e5e04dbef678323e9be6b7329f39049d2c4 (patch)
treeaaed5236c5d78d30cb74fd0109cf60fec6c08a83 /gdb/top.h
parentffd894b51dc68c87f88ae0b09fc90e9bb272aa08 (diff)
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gdb: remove static buffer in command_line_input
[I sent this earlier today, but I don't see it in the archives. Resending it through a different computer / SMTP.] The use of the static buffer in command_line_input is becoming problematic, as explained here [1]. In short, with this patch [2] that attempt to fix a post-hook bug, when running gdb.base/commands.exp, we hit a case where we read a "define" command line from a script file using command_command_line_input. The command line is stored in command_line_input's static buffer. Inside the define command's execution, we read the lines inside the define using command_line_input, which overwrites the define command, in command_line_input's static buffer. After the execution of the define command, execute_command does a command look up to see if a post-hook is registered. For that, it uses a now stale pointer that used to point to the define command, in the static buffer, causing a use-after-free. Note that the pointer in execute_command points to the dynamically-allocated buffer help by the static buffer in command_line_input, not to the static object itself, hence why we see a use-after-free. Fix that by removing the static buffer. I initially changed command_line_input and other related functions to return an std::string, which is the obvious but naive solution. The thing is that some callees don't need to return an allocated string, so this this an unnecessary pessimization. I changed it to passing in a reference to an std::string buffer, which the callee can use if it needs to return dynamically-allocated content. It fills the buffer and returns a pointers to the C string inside. The callees that don't need to return dynamically-allocated content simply don't use it. So, it started with modifying command_line_input as described above, all the other changes derive directly from that. One slightly shady thing is in handle_line_of_input, where we now pass a pointer to an std::string's internal buffer to readline's history_value function, which takes a `char *`. I'm pretty sure that this function does not modify the input string, because I was able to change it (with enough massaging) to take a `const char *`. A subtle change is that we now clear a UI's line buffer using a SCOPE_EXIT in command_line_handler, after executing the command. This was previously done by this line in handle_line_of_input: /* We have a complete command line now. Prepare for the next command, but leave ownership of memory to the buffer . */ cmd_line_buffer->used_size = 0; I think the new way is clearer. [1] https://inbox.sourceware.org/gdb-patches/becb8438-81ef-8ad8-cc42-fcbfaea8cddd@simark.ca/ [2] https://inbox.sourceware.org/gdb-patches/20221213112241.621889-1-jan.vrany@labware.com/ Change-Id: I8fc89b1c69870c7fc7ad9c1705724bd493596300 Reviewed-By: Tom Tromey <tom@tromey.com>
Diffstat (limited to 'gdb/top.h')
-rw-r--r--gdb/top.h8
1 files changed, 4 insertions, 4 deletions
diff --git a/gdb/top.h b/gdb/top.h
index 29778f6..cbe5043 100644
--- a/gdb/top.h
+++ b/gdb/top.h
@@ -68,7 +68,7 @@ struct ui
/* The UI's command line buffer. This is to used to accumulate
input until we have a whole command line. */
- struct buffer line_buffer;
+ std::string line_buffer;
/* The callback used by the event loop whenever an event is detected
on the UI's input file descriptor. This function incrementally
@@ -289,9 +289,9 @@ extern void show_commands (const char *args, int from_tty);
extern void set_verbose (const char *, int, struct cmd_list_element *);
-extern char *handle_line_of_input (struct buffer *cmd_line_buffer,
- const char *rl, int repeat,
- const char *annotation_suffix);
+extern const char *handle_line_of_input (std::string &cmd_line_buffer,
+ const char *rl, int repeat,
+ const char *annotation_suffix);
/* Call at startup to see if the user has requested that gdb start up
quietly. */