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libssh2_userauth_keyboard_interactive_ex.md: fix allocator requirement

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Prior to this patch, the documentation stated that the `.text` buffers
filled by the API caller are "free(3)d" by libssh2, referring to the
default system deallocator. In reality however, libssh2 was using
`SSH2_FREE*()` to free these buffers, respecting custom allocators, if
set by the user via `libssh2_session_init_ex()`.

libssh2 behaved this way since the initial implementation committed in
da653774aa 2005-06-11, v0.11

Later, examples were added that use `strdup()` to allocate, which was
(and is) accurate because they do not use a custom allocator:
9a1ce06e31 2007-07-22

Then, when the documentation landed, it incorrectly documented
`free(3)`, perhaps basing it on the examples added earlier:
d4aa801f6f 2008-03-08

I assume that callers overriding the custom allocators are more likely
to have fixed their code to adhere with how libssh2 actually behaved,
rather than believing the documentation and live with an allocator
mismatch for all these years.

Therefore I think this is a documentation error, and this patch
addresses this.

Reported-by: Makise Kurisu
Fixes GHSA-p6p8-66vc-3f24
Reverts ce631aafe1 #2659
Follow-up to d4aa801f6f
Follow-up to da653774aa

Closes #2661
This commit is contained in:
Viktor Szakats
2026-10-07 13:36:21 +02:00
parent ce631aafe1
commit 59329f3402
2 changed files with 8 additions and 7 deletions
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11
docs/libssh2_userauth_keyboard_interactive_ex.md
View File

@@ -36,11 +36,12 @@ for.
*username_len* - Length of username parameter.
*response_callback* - As authentication proceeds, the host issues several
(1 or more) challenges and requires responses. This callback is called at
this moment. The callback is responsible to obtain responses for the
challenges, fill the provided data structure and then return
control. Responses are sent to the host. String values are free(3)ed
by the library. The callback prototype must match this:
(1 or more) challenges and requires responses. This callback is called at this
moment. The callback is responsible to obtain responses for the challenges,
fill the provided data structure and then return control. Use the custom
LIBSSH2_ALLOC_FUNC (or, if not set, the default system allocator) to allocate
memory for the `text` field. Responses are sent to the host. The callback
prototype must match this:
~~~c
void response(const char *name,

4
include/libssh2.h
View File

@@ -218,14 +218,14 @@ typedef off_t libssh2_struct_stat_size;
#endif
typedef struct _LIBSSH2_USERAUTH_KBDINT_PROMPT
{
unsigned char *text; /* FIXME: require LIBSSH2_ALLOC_FUNC */
unsigned char *text;
size_t length;
unsigned char echo;
} LIBSSH2_USERAUTH_KBDINT_PROMPT;
typedef struct _LIBSSH2_USERAUTH_KBDINT_RESPONSE
{
char *text; /* FIXME: require LIBSSH2_ALLOC_FUNC */
char *text;
unsigned int length; /* FIXME: change type to size_t */
} LIBSSH2_USERAUTH_KBDINT_RESPONSE;