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Rework get_string() to make it more robust when fetching strings of unknown

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length.  In particular, instead of blinding fetching 1k blocks, do an initial
fetch up to the end of the current page followed by page-sized fetches up to
the maximum size.  Previously if the 1k buffer crossed a page boundary and
the second page was not valid, the entire operation would fail.
This commit is contained in:
John Baldwin 2015-08-05 18:14:01 +00:00
parent 7582c8ea08
commit abb3f965d1
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=286331
1 changed files with 29 additions and 17 deletions
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46
usr.bin/truss/syscalls.c
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@ -539,44 +539,56 @@ get_struct(pid_t pid, void *offset, void *buf, int len)
}
#define MAXSIZE 4096
#define BLOCKSIZE 1024
/*
* get_string
* Copy a string from the process. Note that it is
* expected to be a C string, but if max is set, it will
* only get that much.
*/
static char *
get_string(pid_t pid, void *offset, int max)
get_string(pid_t pid, void *addr, int max)
{
struct ptrace_io_desc iorequest;
char *buf;
int diff, i, size, totalsize;
char *buf, *nbuf;
size_t offset, size, totalsize;
diff = 0;
totalsize = size = max ? (max + 1) : BLOCKSIZE;
offset = 0;
if (max)
size = max + 1;
else {
/* Read up to the end of the current page. */
size = PAGE_SIZE - ((uintptr_t)addr % PAGE_SIZE);
if (size > MAXSIZE)
size = MAXSIZE;
}
totalsize = size;
buf = malloc(totalsize);
if (buf == NULL)
return (NULL);
for (;;) {
diff = totalsize - size;
iorequest.piod_op = PIOD_READ_D;
iorequest.piod_offs = (char *)offset + diff;
iorequest.piod_addr = buf + diff;
iorequest.piod_offs = (char *)addr + offset;
iorequest.piod_addr = buf + offset;
iorequest.piod_len = size;
if (ptrace(PT_IO, pid, (caddr_t)&iorequest, 0) < 0) {
free(buf);
return (NULL);
}
for (i = 0 ; i < size; i++) {
if (buf[diff + i] == '\0')
if (memchr(buf + offset, '\0', size) != NULL)
return (buf);
offset += size;
if (totalsize < MAXSIZE && max == 0) {
size = MAXSIZE - totalsize;
if (size > PAGE_SIZE)
size = PAGE_SIZE;
nbuf = realloc(buf, totalsize + size);
if (nbuf == NULL) {
buf[totalsize - 1] = '\0';
return (buf);
}
if (totalsize < MAXSIZE - BLOCKSIZE && max == 0) {
totalsize += BLOCKSIZE;
buf = realloc(buf, totalsize);
size = BLOCKSIZE;
}
buf = nbuf;
totalsize += size;
} else {
buf[totalsize - 1] = '\0';
return (buf);