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Commitf27af7b

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Avoid calling strerror[_r] in PQcancel().
PQcancel() is supposed to be safe to call from a signal handler,and indeed psql uses it that way. All of the library functionsit uses are specified to be async-signal-safe by POSIX ...except for strerror. Neither plain strerror nor strerror_rare considered safe. When this code was written, back in thedark ages, we probably figured "oh, strerror will just indexinto a constant array of strings" ... but in any locale except C,that's unlikely to be true. Probably the reason we've not heardcomplaints is that (a) this error-handling code is unlikely to bereached in normal use, and (b) in many scenarios, localized errorstrings would already have been loaded, after which maybe it'ssafe to call strerror here. Still, this is clearly unacceptable.The best we can do without relying on strerror is to print thedecimal value of errno, so make it do that instead. (This isprobably not much loss of user-friendliness, given that it ishard to get a failure here.)Back-patch to all supported branches.Discussion:https://postgr.es/m/2937814.1641960929@sss.pgh.pa.us
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‎src/interfaces/libpq/fe-connect.c

Lines changed: 19 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -4373,7 +4373,6 @@ internal_cancel(SockAddr *raddr, int be_pid, int be_key,
43734373
{
43744374
intsave_errno=SOCK_ERRNO;
43754375
pgsockettmpsock=PGINVALID_SOCKET;
4376-
charsebuf[PG_STRERROR_R_BUFLEN];
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intmaxlen;
43784377
struct
43794378
{
@@ -4452,8 +4451,25 @@ internal_cancel(SockAddr *raddr, int be_pid, int be_key,
44524451
maxlen=errbufsize-strlen(errbuf)-2;
44534452
if (maxlen >=0)
44544453
{
4455-
strncat(errbuf,SOCK_STRERROR(SOCK_ERRNO,sebuf,sizeof(sebuf)),
4456-
maxlen);
4454+
/*
4455+
* We can't invoke strerror here, since it's not signal-safe. Settle
4456+
* for printing the decimal value of errno. Even that has to be done
4457+
* the hard way.
4458+
*/
4459+
intval=SOCK_ERRNO;
4460+
charbuf[32];
4461+
char*bufp;
4462+
4463+
bufp=buf+sizeof(buf)-1;
4464+
*bufp='\0';
4465+
do
4466+
{
4467+
*(--bufp)= (val %10)+'0';
4468+
val /=10;
4469+
}while (val>0);
4470+
bufp-=6;
4471+
memcpy(bufp,"error ",6);
4472+
strncat(errbuf,bufp,maxlen);
44574473
strcat(errbuf,"\n");
44584474
}
44594475
if (tmpsock!=PGINVALID_SOCKET)

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